Retrofitting a blown film machine based on PLC, touch screen, and frequency converter
Based on PLC, touch screen and inverter on the transformation of blown film machine
Fu Cheng'e, Fan Di Trading (Shanghai) Co., Ltd.
Abstract: Since my country's accession to the WTO, enterprises have faced unprecedented competition in the international market. Therefore, technological innovation aimed at improving product quality and increasing production efficiency is imperative. Traditional industrial control systems suffer from problems such as complex hardware, numerous electrical circuits, difficulties in human-machine interaction, and complex mechanical speed control systems, resulting in heavy maintenance workload, long maintenance times, and poor reliability. This paper utilizes advanced PLC, touch screen, and frequency converter technologies in the field of industrial automation to carry out electrical automation transformation and technological upgrades to plastic blown film machines. This solves the problems of complex operation and long production cycles of traditional control systems, and is beneficial for personnel training and improving the company's market competitiveness.
Chapter 1 Introduction
Plastic blown film machines from Taiwan in the 1980s used a temperature controller and contactor system for their temperature control circuits. Due to frequent high-current switching during operation, the contactors suffered from a very high failure rate. Furthermore, each temperature controller could only control a specific temperature range, resulting in numerous controllers scattered throughout the machine, making operation extremely inconvenient. The control circuit used relay interlocking, leading to complex wiring, difficult maintenance, and very low reliability. Speed adjustment was achieved mechanically, primarily by changing gear reduction ratios, resulting in severe mechanical wear and high energy consumption. These outdated technologies required significant manpower and resources for operation and maintenance, causing long downtime and high spare parts costs. Given that these outdated technologies could not meet production needs and allow the company to maintain a competitive edge in the market, I upgraded the machine using PLCs, touchscreens, and frequency converters, technologies increasingly widely used in industry in recent years. The new technology uses a temperature control module with solid-state relays to control temperature, solving the problem of component damage caused by frequent high-current switching. The frequency converter speed control addresses the issues of severe mechanical wear and high energy consumption. The use of touchscreens allows operators to intuitively understand the machine's current status, solving the problems of complex operation and difficult personnel training. The combined application of these technologies results in high reliability, enabling long-term maintenance-free operation and resolving issues of difficult maintenance and long downtime.
Chapter 2 Design Concept and Selection
2.1 Control Requirements
Due to the global economic recovery, businesses are experiencing a rapid increase in orders and a trend towards product diversification, coupled with the worsening labor shortage in the Pearl River Delta region. Based on this situation, the following requirements are proposed for the control system:
1. The system must be stable and reliable, and able to operate without failure for a long time.
2. It can save multiple recipes and automatically adjust the speed of each motor according to the preset recipe.
3. It should be easy to operate, centrally controlled, and save manpower.
4. It should have fault alarm and protection devices.
2.2 System Analysis
This system primarily utilizes a combination of PLC, touchscreen, and frequency converter to meet the control requirements of the blown film machine. The design concept mainly involves using a PLC temperature control module with solid-state relays to control the temperature of each section of the blown film machine. A PLC analog input module with a frequency converter controls the speed of each motor. A touchscreen is used for setting and displaying temperature, speed, fault settings and displays, and implementing recipe functions, among other things.
2.2.1 Introduction and Workflow Diagram of Blown Film Machine
A plastic blown film machine is a machine that manufactures plastic films from granular plastic raw materials. Its working process is as follows:
Plastic raw material is added to the feed inlet, while the main screw and rotating die head are heated simultaneously. Once the set temperatures are reached, the machine is started. At this point, the plastic raw material, which has been melted at high temperature, is extruded through the annular rotating die head driven by the main screw. The extruded film is then cooled by air and water before being drawn out by the guide roller. After being embossed by embossing rollers A and B, it is guided by the guide roller to the winding roller. Finally, the winding roller rolls the film into finished rolls.
The flowchart and physical diagram are as follows:
Figure 2.1 Flowchart
Figure 2.2 Image of blown film machine
2.2.2 Control Scheme and Approach for the Renovation Project
1. The original method of temperature control using a temperature controller and contactor will be changed to a method using a PLC, a temperature module, and a solid-state relay. Solid-state relays are contactless control devices with a very low failure rate, making them ideal for frequent high-current applications during heating. The PLC-temperature control module method provides stability, accurate temperature control, and centralized temperature control.
2. The original speed regulation method, which involved changing the gear reduction ratio mechanically, was replaced with speed regulation by changing the motor frequency using a frequency converter. Frequency converter speed regulation offers advantages such as energy saving and stability. It also solves the problems of wear and tear and difficult maintenance associated with mechanical speed regulation. Furthermore, by controlling the frequency converter using the analog output function of a PLC, centralized control of the frequency converter is possible, simplifying operation.
3. A touchscreen is used as the host computer to complete various temperature settings, inverter frequency settings, recipe functions, alarm displays, machine fault and status displays, etc. This greatly simplifies operation and saves manpower. The recipe function allows for easy replacement of new products at any time, saving new product launch time and improving efficiency. Alarm and fault displays can inform you of the fault situation and fault location in a timely manner, facilitating maintenance and debugging, while preventing the escalation of the fault.
The following is a control scheme diagram:
Figure 2.3 Control Scheme Diagram
2.2.3 Selection of PLC, Touch Screen and Frequency Inverter
(1) PLC selection
Currently, PLCs can be broadly divided into two schools of thought. One is the Japanese school, represented by brands such as Mitsubishi and Omron.
Another group is the European and American group, mainly represented by Siemens, AB, etc. my country's PLCs are mainly of the Japanese type, including brands such as Xinjie, Yung-Hong, Fengwei, and Delta (Yung-Hong, Fengwei, and Delta are Taiwanese brands).
PLC selection is primarily based on functionality and cost-effectiveness, as more advanced functions generally come at a higher price. This project requires...
The required PLC should have RS485 communication capabilities, expandable modules, and functions such as AD conversion, temperature control, and analog output. Furthermore, the PLC must have a corresponding instruction set, and the company must provide the necessary supporting modules.
Based on the principle of economy and practicality, this project selected Yonghong Motor's FBS-32MAT PLC, FBS-TC6 temperature control module, FBS-4DA analog output module, FBS-6AD analog input module and FBS-CB5 communication module.
(2). Selection of touch screen
There are many types of touchscreens on the market, with commonly used brands including FATEK, eView, GE, Proface, HAKKO, WEINVIEW, and HITECH.
Similar to PLCs, the selection of touchscreens is also determined by functionality and cost-effectiveness; the more features, the higher the price. Almost all brands can provide the functions required for this project. Therefore, based on the principle of economic practicality, the relatively inexpensive FATEK FV070ST-T50 touchscreen was selected for this project.
(3). Selection of frequency converter
Several points to consider when selecting a frequency converter:
1) The purpose of using frequency converters: constant voltage control or constant current control, etc.
2) The load type of the frequency converter; such as vane pump or positive displacement pump, etc. Pay special attention to the performance curve of the load, as the performance curve determines the application method.
3) Matching issue between the frequency converter and the load;
I. Voltage matching; the rated voltage of the frequency converter matches the rated voltage of the load.
II. Current Matching: For ordinary centrifugal pumps, the rated current of the frequency converter matches the rated current of the motor. For special loads such as deep-water pumps, it is necessary to refer to the motor performance parameters to determine the frequency converter current and overload capacity based on the maximum current.
III. Torque matching; This situation may occur under constant torque loads or with a speed reduction device.
4) When using a frequency converter to drive a high-speed motor, the output current increases due to the low reactance of the high-speed motor and the increase in higher harmonics. Therefore, the capacity of the frequency converter used for high-speed motors should be slightly larger than that used for ordinary motors.
5) If the frequency converter is to be operated with a long cable, measures should be taken to suppress the influence of the coupling capacitance between the long cable and the ground to avoid insufficient output of the frequency converter. Therefore, in this case, the capacity of the frequency converter should be increased by one level or an output reactor should be installed at the output end of the frequency converter.
6) For some special applications, such as high temperature and high altitude, the inverter capacity will be reduced, and the inverter capacity will need to be increased by one level.
Based on the above requirements and the actual conditions of this project, the frequency converters selected for this project are all from the Blue Ocean Huateng V5 series. See the diagram below:
Figure 2.6 Blue Ocean Huateng V5 Series Frequency Inverter
Chapter 3 Application Design and Function Implementation
3.1 Design of Human-Machine Interaction via Touch Screen and PLC
To achieve human-machine interaction between the touch screen and the PLC, it is necessary to ensure normal communication between the PLC and the touch screen, and at the same time, the various components on the touch screen must correspond one-to-one with the various software components on the PLC.
3.1.1 Connection Instructions for FBS Series PLC and Yonghong FV Series Touch Screen
Figure 3.1 Settings diagram of Yung-Hong Touchscreen Software Touch Master
The screen editing software for the FV series touchscreen is "Touch Master". Figure 3.1 above shows the settings in "Touch Master" for communication between the Yung-Hong touchscreen and the FBS series PLC. Figure 3.2 is a detailed wiring diagram for communication between the FV series touchscreen and the FBS series PLC, using the RS232 communication protocol.
Figure 3.2 RS232 communication wiring diagram between the touch screen and the FBS host
3.2 Implementation of Temperature Control
This project requires temperature control within a certain accuracy range. The set temperature value is input via a touchscreen, and the temperature value is monitored through the touchscreen screen.
3.2.1 Wiring diagram of PLC temperature control module FBS-TC6
The function of the temperature control module is to convert the temperature signal sensed by the thermocouple into a digital signal and send it to the PLC. The accuracy of the temperature measurement is related to the module's resolution; the higher the resolution, the higher the accuracy. The following diagram shows the wiring diagram of the FBS-TC6.
Figure 3.3 Wiring diagram of PLC temperature control module FBS-TC6
3.2.3 Touchscreen temperature control screen
Figure 3.4 shows the temperature control screen on the touchscreen. In the figure, "Settings" is used to set the desired temperature value, "Sensed Values" is used to display the temperature value detected by the FBS-TC6, and "Manual Heating" is used to select the heating switch.
Figure 3.6 Touchscreen temperature control screen
The "Sensed Value" in the image above displays the temperature value detected by the FBS-TC6. This is the converted value obtained from the on-site measurement by the FBS-TC6. The conversion is necessary because the measured value obtained by the FBS-TC6 is an engineered value; to display the actual temperature in °C, conversion is required. It's important to note that the decimal point on the touchscreen is only an illusion; the actual integer used in the program calculation is an integer. For example, if the touchscreen is set to 33.3, the PLC will use 333 for the calculation.
3.2.4 The logic of the PLC temperature control program
Currently, the most scientific method for PLC temperature control is PID control. PID controller parameter tuning is a core aspect of control system design. It involves determining the proportional gain, integral time, and derivative time of the PID controller based on the characteristics of the controlled process. There are many methods for PID controller parameter tuning, broadly categorized into two types: First, theoretical calculation tuning. This method primarily relies on the system's mathematical model to determine the controller parameters through theoretical calculations. However, the calculated data obtained using this method may not be directly usable and must be adjusted and modified through practical engineering applications. Second, engineering tuning methods. These methods rely heavily on engineering experience and are performed directly in the control system's testing. These methods are simple, easy to master, and widely used in practical engineering.
There are three main engineering methods for tuning PID controller parameters: the critical proportional method, the response curve method, and the decay method. Each method has its own characteristics, but they all involve tuning the controller parameters through experimentation and then applying empirical formulas. However, regardless of the method used, the controller parameters obtained require final adjustment and refinement during actual operation. Currently, the critical proportional method is generally used. The steps for tuning PID controller parameters using this method are as follows:
(1) First, pre-select a sufficiently short sampling period for the system to work;
(2) Add only the proportional control loop until the system exhibits critical oscillation in response to the step input, and record the proportional amplification factor and the critical oscillation period at this point;
(3) The parameters of the PID controller are calculated using formulas under a certain degree of control.
Common problems and solutions in PID temperature control systems:
1. The temperature reaches the target value very quickly, but the temperature overshoot is large.
Analysis: A. The proportional coefficient is too large, resulting in an excessively high heating ratio before the set temperature is reached.
B. The differential coefficient is too small, resulting in insensitivity to the object's response.
Countermeasures: Reduce the proportional coefficient or increase the differential coefficient.
2. The heating often fails to reach the target value, and the temperature remains below the target value for a considerable period of time.
Analysis: A. The proportional coefficient is too small, and the heating ratio is insufficient.
B. The integral coefficient is too small, resulting in insufficient compensation for constant deviation.
Countermeasures: Increase the proportional coefficient or increase the integral coefficient.
3. It is basically on the target, but the deviations are large and it fluctuates frequently.
Analysis: A. The integral coefficient is too small, which means it is not quick enough to respond to immediate changes and the response measures are ineffective.
B. An excessively large integral coefficient causes the differential reaction to be submerged and deactivated.
C. The set basic timing cycle is too short, and the heating has not had time to reach the temperature measuring point.
Countermeasures: Change the integral coefficient and adjust the basic timing period.
4. It is greatly affected by the working environment, and even slight changes will cause temperature fluctuations.
Analysis: A. The integral coefficient is too small, which means it is not quick enough to respond to immediate changes and the response measures are ineffective.
B. The set basic timing period is too long and cannot be corrected in time.
Solution: Change the differential coefficients and adjust the basic timing period.
3.3 Implementation of Motor Speed Regulation
Touchscreen, PLC, and frequency converter are used to control motor speed in the following ways: 1. The touchscreen inputs the set motor speed and displays the current motor speed. 2. The PLC's analog output module FBS-4DA outputs a 0-10V voltage to control the frequency converter's output frequency. 3. The frequency converter drives the motor to start and stop.
3.3.1 Wiring diagram of PLC analog output module FBS-4DA
The function of an analog output module is to convert digital signals from a PLC into analog signals and output voltage or current. The diagram below shows the wiring diagram of the Yonghong Motor FBS-4DA analog output module. The 0-10V voltage output from the O0+ and O0- terminals is connected to the 0-10V analog input terminals of the frequency converter to control the frequency converter speed.
3.3.3 Touchscreen speed control screen
The image below shows the speed control screen on the touchscreen, primarily used to control the speed of each motor. The OFF button is used to turn the corresponding motor on and off. Button A is used to set and display the motor frequency setting. Button B displays the current operating frequency of the motor. The "Accelerate" and "Decelerate" buttons are used to fine-tune the motor frequency during operation.
The "Motor Frequency Setpoint" is the motor frequency required on-site, provided by the touchscreen to the PLC host. This is a current value, which needs to be calculated by the PLC host program to obtain an engineering value from 0 to 250 based on the actual situation. This engineering value is then assigned to the FBC-4DA module, which in turn converts it into an analog voltage or current signal to control the frequency converter. Note the decimal point issue on the touchscreen here as well.
3.3.4 Wiring and Setup of the Frequency Converter
Inverter wiring diagram:
Inverter settings
The parameter setting methods for frequency converters vary from brand to brand, but they all follow the same principles, mainly in the following aspects:
1. Set the frequency command source. In this project, the main frequency input should be set to be controlled by the analog signal DC 0-+10V (AVI).
2. Source of operation commands: This project is configured so that operation commands are controlled by external terminals.
3. Motor stopping method: This project sets it to free stop.
4. The maximum operating frequency is set to 100Hz in this project.
5. Maximum output voltage, set to 220V for this project.
Other functions, such as acceleration/deceleration time and anti-reverse settings, also need to be set according to the actual situation.
in conclusion
The integrated application of PLC, touch screen, and frequency converter automatic control technology improves the quality of industrial products and the efficiency of production equipment. It solves problems such as the complexity of traditional control systems and long production cycles for new products, and is beneficial for personnel training and enhancing enterprise market competitiveness. This paper, based on actual production conditions, describes the modification of a plastic blown film machine. The integrated control technology of PLC, touch screen, and frequency converter was used to control temperature and speed, improving the reliability of electrical control, shortening maintenance time, reducing maintenance workload, and lowering the damage rate of equipment parts. Therefore, this technology should be widely applied in modern industry and has broad development prospects.
