The dyeing process occupies an important position in textile production. The quality of the dyeing directly determines the color and appearance of the textile, and even affects the production cost of the textile. In the dyeing process, the main factors affecting dyeing are dye liquor concentration, temperature, liquid level, etc., of which temperature control is a very important and complicated control process. The dyeing process is actually a temperature curve executed by the craftsman for different fabrics. Each process has strict requirements for the temperature of the dyeing and the temperature rise and fall process. Otherwise, it is easy to cause defects such as chromatic aberration, cylinder difference, streak, etc., resulting in an increase in counter-dyeing rate and an increase in production cost. In view of the complexity of temperature control in the dyeing process, a temperature control system for the dyeing machine based on PLC was designed to achieve temperature control in the dyeing process, thereby reducing fabric defects, improving production efficiency, and reducing production costs.

System control requirements

1. Temperature curve storage requirements For different dyeing varieties, the temperature requirements are different, so the corresponding temperature process curve is also different. This system uses the configuration formula design of the touch screen to store various dyeing processes and the data of different stages in each set of processes in the touch screen, so that it is more convenient for the process personnel to operate. Technicians can modify and save the process parameters at any time, and this data will be permanently kept in the touch screen. The different temperature process curves set by the process personnel are all input by the worker on the touch screen, and the controller performs temperature control according to the received temperature process curve. Both the controller and the touch screen have the function of saving current data for a long time after power off.

2. Temperature control requirements. During the dyeing process, the typical process curve is as follows:

　　Figure 1 Typical process curve

It can be seen from Figure 1 that the dyeing process can be divided into multiple curve segments, and different curve segments correspond to different temperatures. The temperature control of the dyeing process is mainly to allow the dye solution in the cup on the core to heat up, keep warm, and cool down. Combined with the actual requirements of production, the temperature-increasing stage is set according to the slope. The PLC setting during temperature rise can be 0-9°C, this rate needs to be calculated according to the power of the heater on site. The heater was already running at full power when it was set to 4°C during the field test. This kind of humanized slope temperature rise selection is set in the PLC, so that the temperature rise stage is well set. The temperature control is divided into five subroutines: according to direct heating, slope heating, heat preservation, direct cooling and cooling process according to slope. These five processes correspond to five sections of programs in the PLC, and then execute cyclically according to the selection of the upper step number. As shown in Figure 2, Figure 3:

　　Figure 2: Dyeing recipe interface

　　Figure 3: The main interface

3. Alarm display and dyeing recipe function. Figures 2 and 3 above are the two most important interfaces during operation. In order to allow users to better view the various statuses in operation, a curve chart is made on the main screen to more intuitively view the effect of process temperature. The dyeing recipe process interface allows users to more easily set up various processes and choose to run. This system sets 9 steps for each process, and can set the step number of operation, and run from this step number. When a set of processes is completed, the main interface pops up that a set of dyeing processes has been completed. Please confirm, the user can proceed to the next set of process after confirming. As shown below.

　　Figure 4: Confirmation of the end of a process

The interface on the right side in Fig. 4 is mainly the control of the motor speed and the control of the frequency conversion forward and reverse. In addition to the manual setting of the speed control, the control of forward and reverse rotation, forward rotation time, reverse rotation time and stop time are all realized by PLC programming. When various faults occur, the touch screen indicator flashes, and a fault alarm occurs, and a fault alarm screen pops up to show the cause of the alarm.

The hardware configuration of the system

This system uses NA200 small PLC as the field controller. NA series programmable controller is a new generation of control device with international advanced level which is newly developed by Nanda Automation Technology Co., Ltd. It uses a series of latest achievements in the field of industrial control, selects a brand-new software and hardware platform, has fast processing capabilities, powerful anti-jamming performance, flexible and scalable functions. For any complex environment and processing requirements, you can easily handle and cope with it. More than 20 years of experience in the development of automation products and on-site testing of hundreds of projects have created the reliable quality of Nanda Automation PLC. The products have passed the CE certification, CCS certification and the rigorous testing and inspection of the power industry power system automation equipment quality inspection and testing center. Each performance index meets or exceeds the requirements of related standards, leading the similar products.

Select CPU2002 host module. Connect the touch screen via RS232 port modbus-rtu protocol. The field controller has expanded an intelligent temperature data acquisition module RTD input module 2 channels. The module has 2 analog input points and no external transmitter is required. One module can complete data collection and data processing functions. The detection of the temperature signal of the system uses a platinum resistance PT100. The platinum resistance has the characteristics of high measurement accuracy, stable and reliable performance, and is widely used in industry for temperature measurement between -200°C and +500°C.

In addition, if necessary, you can connect the PLC to the factory monitoring through the RS485 interface, MODBUS-RTU, to achieve remote operation and monitoring.

Part of the configuration of the control system: one CPU2002 (Nanda Automation), one RTD input module 2 channels (Nanda Automation), 7-inch touch screen (Nanda Automation).

System software design

It can be seen from Figure 1 that the dyeing process can be divided into several curve segments, and different curve segments correspond to different target temperatures, temperature rise and fall times, and heat preservation times. The temperature control of the dyeing process is mainly to heat, heat, and cool the dyeing tank. Combined with the actual requirements of production, the temperature is divided into direct temperature increase to the specified temperature and accurate temperature increase to the specified temperature according to the slope. In the same way, cooling is also divided into direct cooling to the specified temperature and accurate cooling to the specified temperature according to the slope. Therefore, temperature control is divided into five subroutines: direct heating, heating according to slope, heat preservation, direct cooling, and cooling according to slope. Direct heating or slope heating, direct cooling or slope cooling are set by the central control machine according to actual needs, and then the corresponding subroutine is called by the main program of the field controller PLC.Due to the large volume of the dyeing tank, the heating pipe is relatively small, resulting in a relatively large temperature inertia. Generally, it can be regarded as a controlled object with pure lag and large inertia. Therefore, the trend judgment compensation method is adopted in the rising/cooling section. If it is a temperature rise, the temperature rise is stopped when the temperature reaches the target temperature of T set value -△Ti, where △Ti is the compensation temperature. In the main program of PLC, it is judged according to the data received from the touch screen, and then the corresponding program is executed. The download data includes target temperature, slope, holding time, etc. Therefore, the PLC can judge whether to heat up, keep warm, or cool down based on these values. However, when judging heating, cooling, and heat preservation, the target temperature, slope, and heat preservation time cannot be used to accurately judge, so the target temperature of the previous curve segment is used to assist the judgment.

The following uses the ramp temperature as an example to illustrate the PLC temperature control process. When ramping up the temperature, the temperature-increasing section curve is divided into several equal small intervals according to time, so the temperature-increasing section of the process curve can be expressed in steps. As long as the time of each interval is sufficiently small, the deviation between the calculated temperature setpoint and the ideal value of each interval can be ignored.

Due to the large hysteresis of the temperature, when the actual temperature T is close to the set temperature, a waste heat rise setting is made at this time, so as to ensure that the temperature will not be excessively high during the warming up to the holding stage.

In addition, because the temperature measurement of PT100 is only one point of the dyeing tank, the temperature measurement is not necessarily the temperature of the dye solution in the final cup, so the temperature compensation △Ti is set to better meet the process requirements. The temperature rise curve is shown below:

Figure 5: The slope of different heating rate is shown in the figure (the slope is 3℃/min and 2℃/min).

In order to better ensure the security of the system, the system has added permission settings and set a variety of permissions: super administrator (with all permissions), process personnel, etc., these can be freely customized according to your requirements.

　　Figure 6: User login interface

The content of the dyeing formula design greatly simplifies the problem of simple and rough interface for controlling the computer with the dyeing machine and difficult operation. As shown in the figure below, customize your process recipes directly on the touch screen.

　　Figure 7: Dyeing process recipe editing

This system can not only realize temperature control, but also expand the control of other dyeing processes such as water level, liquid level and other parameters according to needs, and has good development prospects. This system uses PLC as the controller of the production site to complete the temperature control, which can control the quality of the dyed products in time and accurately, eliminate the hidden dangers of the product quality on the site, and ensure the consistency of dyeing and one-time accuracy. Compared with the traditional dyeing machine control computer, the advantages of using PLC control are mainly reflected in:

PLC control makes the system more stable and reliable.

Using touch screen to operate, the operability is quite convenient, the effect is more intuitive, making your whole system more flexible.

The dyeing process recipe greatly enhances the operability and intuitiveness, saving your precious time, manpower and material resources.

The advantage of PLC control is also greater flexibility, so that if you need to improve or add a new system process. Only you need to maintain the program, which saves you a lot of money to buy a new dyeing machine control computer! The touch screen interface can be customized freely according to your requirements.