Abstract: An automatic batching control system using an OMRON PLC as the main controller was designed. This system achieves automatic feeding control via a frequency converter and boasts advantages such as high precision, good feasibility, and strong anti-interference capability. The host computer utilizes KingSCADA software for real-time online monitoring, enabling timely access to field information, sending control commands, real-time material loading, and viewing historical and real-time data and curves. Furthermore, the system can transmit production data to the decision-making management layer via the WEB publishing function of the configuration interface. The decision-making management layer then publishes the production formula down to the production management layer, achieving effective connection of information across all levels of the enterprise and realizing a certain degree of integrated management and control. Serial communication and configuration software I/O drivers were developed using VC++, enabling the exchange of real-time data between the PLC and the field.
Keywords: Automated batching monitoring system, configuration interface, integrated management and control
1. Introduction
In modern industrial production, it is often necessary to mix multiple raw materials in a certain proportion to manufacture a certain product. This batching and weighing system, which mixes one raw material with several other raw materials in a pre-set proportion, has a wide range of applications in industrial production. It can weigh and batch various raw materials in different weighing equipment according to a pre-set batching list.
Steelmaking protective slag is a commonly used material in modern steelmaking metallurgy, directly affecting the quality of steel billets during casting and solidification. The protective slag is prepared from eight materials in a specific ratio: limestone, glass powder, graphite, cement, industrial sodium chloride, and soda ash. The accuracy of the batching significantly impacts the quality of the steel billets. Therefore, precise and efficient weighing equipment not only improves productivity but also ensures the production of high-quality protective slag.
Based on the steelmaking protective slag batching process in the metallurgical industry, this automatic batching system was developed and designed, and can be remotely monitored via network.
2. Feasibility Study
2.1 System Process Flow
Steelmaking protective slag is prepared by mixing eight materials—limestone, glass powder, graphite, cement, industrial sodium chloride, and soda ash—in a specific ratio. The process flow of the batching system is shown in Figure 1. The storage silos control the feeding of the eight materials into eight separate storage bins. These eight bins form a circle above a conical central funnel (only two bins are shown in the figure). The materials are sequentially fed into an electronic scale through the central funnel for weighing. The storage silos are divided into upper and lower feeding bins. The eight materials are placed in the eight upper feeding bins, and a screw feeder is connected to the lower opening of the lower feeding bins. To prevent the screw feeder from being "crushed" by the material, upper and lower resistance level gauges are installed in the lower feeding bins. When the material is at the lower feeding level, the valve between the upper and lower feeding bins is opened to allow the material to enter the lower feeding bin; when the material reaches the upper feeding level of the lower feeding bin, this valve is closed. The automatic batching process control system first starts the No. 1 screw feeder, continuously feeding the electronic scale at full speed, and the scale continuously weighs the material. When a certain weighing value is reached, the screw feeder speed begins to decrease (variable frequency speed control). As the material increases, the screw feeder speed becomes slower and slower. When the weighing value approaches or reaches the required value, the screw feeder stops, at which point the weighing of each material is complete. Open the electronic scale discharge valve and place the material into the intermediate storage silo for temporary storage. Then start the #2 feeder to weigh the second type of material. After each type is weighed, place it into the intermediate storage silo for temporary storage. After all eight types of materials have been weighed, put them into the ball mill together, add water to mix, and then send them to the next process.
2.2 Comparison of Schemes
Currently, there are three types of automatic batching solutions: automatic devices with a microcontroller as the main controller, automatic batching devices with a PLC as the main controller, and intelligent automatic batching devices. The advantages and disadvantages of each method are as follows:
(1) Automatic device with a microcontroller as the main controller
In modern industrial production, automated devices using microcontrollers as controllers are emerging in large numbers and widely used in industrial control. Microcontrollers dominate the market due to their low price and lightweight design, and their functions and development tools are relatively complete. However, systems developed using microcontrollers are difficult to maintain in the later stages. Intelligent control devices developed using microcontrollers are low-cost, easy to develop, and flexible in function, with a mature development system and comprehensive features. However, their anti-interference capabilities are limited, making them unsuitable for harsh industrial environments. They can communicate with computers, but require complex programming. Due to the limitations of microcontroller technology, it is difficult to create more advanced unified control interfaces.
(2) Automatic batching device with PLC as the main controller
A control system composed of PLCs offers relatively stable performance, strong anti-interference capabilities, meets industrial-grade standards, and is suitable for harsh industrial environments. The number of input/output points of a PLC can be flexibly configured, and additional inputs/outputs can be freely added.
Its strong logic control capabilities allow for long-term operation in industrial settings, and it boasts high self-protection capabilities. It can establish communication with a host computer to exchange data, or exchange data via a network through a serial port internet module. Its comprehensive functions, flexible configuration, simple programming, and reliable operation make it widely used in industrial settings. Due to the maturity of PLC technology, it is easy to create upper-level monitoring pages.
(3) Dedicated automatic batching device
Professional automatic batching devices are simple and easy to use, suitable for small-scale control applications, and can fulfill simple control requirements with high accuracy. However, dedicated instruments are expensive, hindering system expansion. Expanding and maintaining molding systems is quite difficult. In industrial control, they are unsuitable for controlling production data that fluctuates frequently and complex logic algorithms. In industry, they are often used as field intelligent I/O to directly control field devices and transmit simple data to larger, higher-level intelligent control equipment via data cables.
The three commonly used industrial control schemes mentioned above can be used to obtain automatic devices and intelligent automatic batching devices with single-chip microcomputers as the main controllers. However, these are difficult to meet the requirements of this design. Therefore, an automatic batching system scheme with PLC as the main controller is selected.
Figure 1 System process flow
2.3 Automatic batching scheme with PLC as the main controller
(1) Framework and Concept
On-site control section:
Based on the steelmaking protective slag batching process and field devices (valves, feeders, level gauges, weighing sensors, etc.), the number of controllable I/O points (specifically divided into digital and analog signals) is determined. By selecting an appropriate PLC model, the batching logic control is completed. The PLC receives the batching volume from the host computer, and through the input of switch signals into the host computer's configuration software, the PLC automatically completes the logic calculations and controls the frequency of each batching inverter to drive the corresponding feeder.
Process Management Section:
The host computer uses configuration software to monitor the field operation status in real time, obtain field I/O data promptly, and send control commands as needed. The host computer configuration software is used to store data, display real-time data curves, and display historical data curves. Through the configured web publishing function, data is transmitted to the upper-level management department, which then receives control commands.
(2) Selection of system equipment
The system requires 8 analog outputs, 1 analog input, 28 digital inputs, and 12 digital outputs, so the OMRON CQM1H series PLC is selected.
Inverter: Delta VFD-A 2.2Kw 8 units; Load cell: Kunlun Coast Company BK-5 type cantilever beam force/weighing sensor, pressure sensor, weighing range: 0-20t.
Level gauge: UL-3LP series resistance level gauge manufactured by Liaoning Zhongxin Automation Instrument Co., Ltd. Detection principle: When the detection plate is obstructed, an alarm signal is output, and the relay state changes; when the material leaves the detection plate, the detection state is restored; reciprocating frequency: times/min; output power saving capacity: standard type AC220V•5A, horizontal installation, pressure resistance <0.3Mpa; screw feeder: XGL150, power is 1.5Kw, material bucket diameter is 160mm.
3. System Design
3.1 PLC Programming
This system uses a CQM1H PLC, and its programming language is ladder logic. The software of the automatic weighing control system is divided into two parts: one part is the material level control software for the silo, and the other part is the control software for the weighing system.
(1) Material level control software for silos:
The material level control system has a total of 8 storage silos. When the material is at the unloading position, the valve between the unloading and loading silos is opened to put the material into the unloading silo; when the material reaches the loading position of the unloading silo, the valve is closed.
(2) Automatic weighing control software
Because this system does not allow for weight overshoot, general control methods cannot be used. To meet the requirements of weighing accuracy and speed, this system employs a saturated nonlinear method. The limit value of Uk is 10V. Since the weight of each material varies, the values of Up and K1 also differ. When feeding begins, Upf is relatively small, Uk = KΔU = Ukmax, and the screw feeder feeds at full speed. When Upf reaches a certain value, Uk = K1ΔU < Ukmax, but Uk > Umin. At this point, Uk is a low-speed setpoint. As Upf gradually increases, Uk gradually decreases. When Uk = Umin, feeding stops, and weighing is complete.
3.2 Configuration Program Design
Configuration software can easily draw up the on-site working environment and realistically simulate the on-site working conditions, which is conducive to centralized industrial monitoring.
(1) Introduction to configuration
The general process for establishing a new configuration project is as follows:
Design the graphical interface (define the screen);
Define the device; construct the database (define variables);
Establish animation links;
Run and debug.
It should be noted that these five steps are not entirely independent; in fact, these four parts are often intertwined. When developing a project using the KingSCADA graphical development system, three aspects should be considered according to this process:
Graphics: What kind of graphical interface do users want? In other words, how can abstract graphical interfaces be used to simulate actual industrial sites and corresponding industrial control equipment?
Data: How can data be used to describe the various attributes of industrial control objects? That is, to create a specific database in which variables reflect the various attributes of industrial control objects, such as temperature and pressure.
Connection: What are the connection relationships between the elements in the data and graphics screen? In other words, how do the elements on the screen animate to simulate the operation of the field equipment, and how do they allow the operator to input commands to control the equipment?
(2) Main screen function
The main screen is the primary monitoring interface of the system, as shown in Figure 2. It displays real-time field data. The screen displays the actual material ratio of the current batching and the given material ratios of the eight materials. After each batching cycle is completed, the actual batching value is displayed in real time. The actual value of the current batching can be directly displayed. The third row of the table shows the system's error for each material. According to requirements, this error should be less than 5%. Otherwise, it will affect the quality of the steelmaking protective slag and may affect actual production. The calculation of this error is implemented in the application script. The script language refreshes the screen every 3 seconds when the configuration program is running, and the screen animation changes according to different connection variables.
Figure 2 Configuration Main Interface
Control button descriptions:
Power on: Power on the eight frequency converters in the system to put the system into a ready state;
Start: Press the fully automatic operation button to put the system into automatic operation mode. The eight ingredients of the system will run in sequence. If it does not stop, the system will run in a loop according to the current formula.
Stop: The system can be stopped at any point in its life.
Material selection: From left to right, from high to low, a 3-bit binary number represents one of eight ingredients, allowing operators to perform manual and semi-automatic operations.
Manual: Equivalent to a push-button operation.
Semi-automatic: A single-step operation that performs each ingredient preparation step.
3.3 OMRON PLC Serial Port Driver under Configuration (1) Technical Background With the improvement of modern control technology, online real-time monitoring has become an indispensable part of engineering. This requires the configuration software to exchange data with field devices in real time and transmit production information. Although the PLC program in the configuration software is now relatively complete and can basically meet the needs of users, new serial port devices (PLC, field instruments, flow meters, etc.) are emerging one after another. Some devices do not have drivers under the configuration software, that is, they cannot be connected to the configuration software for the time being. At this time, engineers need to write suitable drivers themselves according to the development interface provided by the manufacturer and the protocol standard provided by the hardware manufacturer.
(2) Driver Overview
The IO driver (FIOS) is responsible for exchanging data with various I/O devices. On one hand, it sends real-time process data collected from I/O devices to the database (DB); on the other hand, download data from the DB is also sent to the I/O devices through FIOS. FIOS has an open architecture, providing development tools and interface standards that allow users to develop drivers for various I/O devices themselves using ForceControl software as a platform.
The FIOS SDK consists of four main parts: device configuration interface (Iodevcfg), data connection configuration interface (Ioitemui), I/O monitoring interface (Ioapi), and I/O server program (Ioserver).
Iodevcfg: Responsible for managing the device configuration process.
Ioitemui: Responsible for managing the data connection configuration process.
IoAPI: Responsible for data exchange with I/O devices and enabling device monitoring. This includes parsing communication protocols and converting data formats.
Ioserver: Dynamically loads the IoAPI portion, calling and executing exported functions implemented by IoAPI. It also handles low-level communication with I/O devices (serial communication, network communication, etc.), as well as device timeout handling and device fault diagnosis. Ioserver further handles communication with the database (DB). It parses and transforms data collected from I/O devices using IoAPI and submits it to the DB, or it parses and transforms data passed from the DB to the I/O devices and writes it to the I/O devices.
Ioserver is provided by the FIOS SDK. Programmers only need to develop code for three parts: Iodevcfg, Ioitemui, and Ioapi.
4. Design Summary
4.1 Design Innovations
This design combines the realities of modern production with current trends in industrial control, boldly proposing innovations based on conventional production control.
In terms of ingredient control, in addition to being able to perform conventional automatic ingredient control, it boldly proposes the function of providing production data to senior management and accepting senior management management, so that production control information can be transmitted to the next level through effective and feasible means and in a safe manner.
This design effectively coordinates internal enterprise information, enables unified scheduling of enterprise resources, and achieves an integrated management and control strategy. Specifically, it allows users to query and statistically analyze relevant variables for a specific time period via a web page, and simultaneously select appropriate formulas based on comprehensive internal enterprise information and store them in a formula storage file.
Regarding the driver program, although the PLC driver program used in this design is relatively complete, in actual engineering applications such as equipment modification and upgrades, some new instruments and PLCs may not be able to be connected to this system configuration. In this case, the current driver design template can be used for simple modification, which facilitates system upgrades and improvements.
4.2 Design Summary
Through the design and practice of designing an automated batching system, I learned some skills and methods, which are summarized below:
(1) PLC programming
The flexible use of PLC bits and channels, and the correspondence between the bits in the channels and the values in the channels, bring convenience to programming.
Sequential programming methods for PLC programming;
When programming complex states in a PLC, the complex state is first decomposed into multiple smaller states, each of which is assigned an auxiliary point. Finally, the logical relationship between the auxiliary points of each smaller state is used to generate the corresponding action.
(2) Configuration aspects
In the process of applying and learning configuration, I not only mastered the commonly used functions of configuration, such as drawing screens, defining IO variables, scripting language, animation connection, data reports, real-time curves, historical curves, and historical alarms, but also accumulated some application skills and methods, and gained a deeper understanding of configuration.
The impact of IO variable linear transformation settings in configuration on data acquisition and command placement; methods for quick setup and modification of web pages, configuration of publishing pages, and specific port number settings in publishing settings;
The specific roles of page, application, and variable refresh rates in the system;
Modifications to graphic elements can be easily made to suit one's needs.
(3) Driver aspects
Having mastered the essential knowledge of driver development, I can now quickly program within a hardware development configuration. I have accumulated experience in VC programming and can use API functions to program some Windows programs.
Once you've learned how to program serial ports using VC++, you can use VC++ to program serial ports, write suitable serial port applications, and complete the corresponding functions.
It can use the force control interface SDK to develop corresponding hardware and write configuration drivers suitable for the hardware;
We can customize solutions for the corresponding hardware drivers and create appropriate drivers.
Familiar with the VC development environment.
