Abstract: This paper applies Nanjing Aotop NA200 PLC and touch screen to realize the automated control of fabric dyeing in the dyeing and finishing industry.
1 Introduction
Dyeing plays a crucial role in textile production, directly determining the color, appearance, and even production costs of textiles. Factors influencing dyeing include dye concentration, temperature, and liquid level, with temperature control being a critical and complex process. The dyeing process essentially involves executing a temperature profile designed by technicians for different fabrics. Each process has strict requirements for dyeing temperature and the temperature rise and fall procedures; otherwise, defects such as color difference, batch variation, and streaks can easily occur, leading to increased re-dyeing rates and higher production costs. To address the complexity of temperature control in the dyeing process, a PLC-based temperature control system for the dyeing machine was designed to control the dyeing temperature, thereby reducing fabric defects, improving production efficiency, and lowering production costs.
2 System Control Requirements
1) Temperature Curve Storage Requirements: Different dyeing varieties have different temperature requirements, thus requiring different temperature process curves. This system uses a touchscreen to configure and design recipes, storing data from various dyeing processes and different stages of each process on the touchscreen. This facilitates operation for process engineers, who can modify and save process parameters at any time. This data is permanently stored on the touchscreen. All different temperature process curves set by the process engineer are input by the operator on the touchscreen, and the controller performs temperature control based on the received temperature process curves. Both the controller and the touchscreen have the function of permanently saving current data even after power failure.
2) Temperature control requirements: In the dyeing process, a typical process curve is shown in Figure 1 below:
Figure 1 Typical process curve
As shown in Figure 1, the dyeing process can be divided into multiple curve segments, each corresponding to a different temperature. Temperature control during the dyeing process mainly involves heating, holding, and cooling the dye solution in the cup on the core. Based on actual production requirements, the heating stage is set according to a slope. The PLC setting for heating can be 0-9℃, and this rate needs to be calculated based on the power of the on-site heater. During the on-site test, the heater was already running at full power when the temperature reached 4℃. This user-friendly slope heating selection in the PLC allows for effective setting of the heating stage. Temperature control is divided into five subroutines: direct heating, slope heating, holding, direct cooling, and slope cooling. These five processes correspond to five program segments in the PLC, which are then executed cyclically according to the selected step number from the host computer. See Figures 2 and 3.
Figure 2-1: Digitally captured interface of dyeing formula
Figure 2-2: Simulation running of dyeing recipe interface
Figure 3-1: Main interface of digital real-shot
Figure 3-2: Simulation Run Main Interface
3) Alarm display and dyeing formula function
Figures 2 and 3 above show the two main interfaces during operation. To allow users to better view various states during operation, a graph is displayed on the main screen, providing a more intuitive view of the temperature effect. The dyeing formula process interface allows users to easily set up and select processes. Each process in this system has 9 steps, and users can set the step number and run from that step number onwards. When a process is completed, a pop-up message appears on the main screen indicating that the dyeing process has finished and requesting confirmation before proceeding to the next process. See the following figure:
Figure 4: Process completion confirmation screen
The interface on the right side of Figure 4 mainly controls the motor speed and the forward and reverse rotation of the frequency converter. Except for the speed control, which is manually set, the forward and reverse rotation control, as well as the forward rotation time, reverse rotation time, and stop time, are all implemented by PLC programming. When various faults occur, the touchscreen indicator lights flash, a fault alarm appears, and a fault alarm screen pops up displaying the cause of the alarm.
3. System Hardware Configuration
This system uses the NA200 small PLC from Nanda Aotuo Technology Co., Ltd. as the field controller. The NA series programmable controllers are the latest generation of control devices developed by Nanda Aotuo Technology Co., Ltd., possessing internationally advanced levels. They incorporate the latest achievements in industrial control, utilize a brand-new hardware and software platform, and feature rapid processing capabilities, strong anti-interference performance, and flexible expandability. They can handle any complex environment and processing requirements with ease. Over twenty years of experience in developing automation products and hundreds of field tests have forged the reliable quality of Nanda Aotuo PLCs. The products have passed CE certification, CCS certification, and rigorous testing and inspection by the Power Industry Power System Automation Equipment Quality Inspection and Testing Center. All performance indicators meet or exceed relevant standards, leading similar products. The CPU2002 host module is selected; the touchscreen is connected via RS232 port using the Modbus-RTU protocol. The field controller is expanded with a smart temperature data acquisition module, an RTD input module with two channels. This module has two analog input points, eliminating the need for external transmitters; a single module can complete data acquisition and processing functions. The temperature signal detection of the system uses a platinum resistance thermometer (PT100). Platinum resistance thermometers are characterized by high measurement accuracy and stable and reliable performance, and are widely used in industry for temperature measurement between -200℃ and +500℃.
Additionally, if needed, the MODBUS-RTU can connect the PLC to the factory monitoring system via the RS485 interface to enable remote operation and monitoring.
The control system is equipped with a CPU2002 (Nanda Aotuo), a 2-channel RTD input module (Nanda Aotuo), and a 7-inch touch screen (Nanda Aotuo).
4. System Software Design
As shown in Figure 1, the dyeing process can be divided into several curve segments, each corresponding to a different target temperature, heating/cooling time, and holding time. Temperature control in the dyeing process mainly involves heating, holding, and cooling the dye bath. Based on actual production requirements, heating is further divided into directly heating to the specified temperature and accurately heating to the specified temperature according to a slope. Similarly, cooling is also divided into directly cooling to the specified temperature and accurately cooling to the specified temperature according to a slope. Therefore, temperature control is divided into five subroutines: direct heating, heating according to a slope, holding, direct cooling, and cooling according to a slope. Whether to use direct heating or slope heating, direct cooling or slope cooling is set by the central control unit according to actual needs, and then the main program of the field controller PLC calls the corresponding subroutines. Due to the large volume of the dyeing vat and the relatively small size of the heating pipes, a significant temperature inertia is generated. It can generally be considered a controlled object with pure time lag and large inertia. Therefore, a trend-based compensation method is used in the heating/cooling stages. If heating is occurring, it stops when the temperature reaches the target temperature T - ΔTi, where ΔTi is the compensation temperature. In the PLC's main program, the data received from the touchscreen is analyzed, and the corresponding program is executed. The transmitted data includes the target temperature, slope, and holding time, allowing the PLC to determine whether heating, holding, or cooling is occurring. However, judging heating, cooling, or holding solely based on the target temperature, slope, and holding time is insufficient; therefore, the target temperature of the previous curve segment is used as an auxiliary factor in the judgment.
The following example of slope-based heating illustrates the temperature control process of a PLC. During slope-based heating, the heating curve is divided into several equal small intervals based on time, thus the heating segment of the process curve can be represented by a step-like structure. As long as the time of each interval is sufficiently small, the deviation between the calculated temperature setpoint and the ideal value for each interval can be ignored.
Due to the large temperature lag, when the actual temperature T is close to the set temperature, a residual heat heating setting is made to ensure that the temperature does not exceed the set temperature during the heating and holding stage.
In addition, since the temperature measurement of PT100 only involves one point in the dye bath, the temperature measurement may not be the final temperature of the dye solution in the cup. Therefore, a temperature compensation ΔTi was set to better meet the process requirements.
The temperature rise curve is shown in the figure below:
Figure 5: The slopes of different heating rates are shown in the figure (slopes are 3℃/min and 2℃/min).
The curve for the heat preservation stage can also be seen in the figure.
To better ensure system security, the system has added permission settings, setting various permissions: super administrator (with all permissions), process personnel, etc., which can be freely customized according to your requirements.
Figure 6: User Login Interface
Figure 7: Logout screen
The dyeing formula design greatly simplifies the problem of the simple and crude computer interface used to control the dyeing machine, which makes operation difficult. As shown in the figure below, you can directly customize your process formula on the touch screen.
Figure 8: Dyeing process formula editing
5 Conclusion <br /> This system can not only achieve temperature control, but also can be expanded to control other dyeing processes as needed, such as water level and liquid level parameters, and has good development prospects.
This system uses a PLC as the controller on the production floor to control temperature, enabling timely and accurate control of the dyed product quality. This eliminates potential quality issues on-site, ensuring dyeing consistency and one-time accuracy. Compared to traditional computer-controlled dyeing machines, the advantages of using PLC control are mainly reflected in:
1) PLC control makes the system more stable and reliable;
2) The touchscreen is easy to use, the effect is more intuitive, and it is also more aesthetically pleasing, making your whole system more flexible;
3) The dyeing process formula has been greatly improved in terms of operability and intuitiveness, saving you valuable time, manpower and resources;
4) The advantage of PLC control also lies in its greater flexibility. If you need to improve or add new processes to the system, you only need to maintain the program, thus saving you the expense of buying a new dyeing machine control computer! The touch screen interface can also be customized according to your requirements.
