Design of control system for jet loom based on PIC16F874 single chip microcomputer

    A textile machine is the full name of a tool that processes raw materials such as thread, silk, and hemp into silk thread and then weaves it into cloth. Such as spinning pendants, spinning wheels, spindles, pedal looms, mechanical looms, CNC automatic looms, etc. The development of textile process and equipment in ancient and modern times is designed in response to textile raw materials. Therefore, raw materials play an important role in textile technology. The fibers used for textiles in ancient countries in the world are all natural fibers, generally three short fibers (wool, hemp, and cotton). When a running textile machine needs to be shut down due to failure, shift change, or other reasons, unevenness between the wefts will occur when it is turned on again. Either the gap between the two wefts is too large or the gap is too small, resulting in defective fabrics. This controller designs a textile machine tightness adjustment controller based on the PIC16F874 microcontroller, which successfully solves this problem. It has the advantages of high precision, reliable and convenient operation, and high cost performance.

　　1 Controller Working Principle

　　The adjustable elastic band controller includes a fixed plate, two left and right horizontal bolt holes are arranged in the fixed plate, a latch part is arranged in front of the fixed plate, the latch part includes a hook arm and a base, the hook arm and the base form a notch, a cantilever and a fixed arm are contained in the notch, the right end of the cantilever is pivotally connected with the right end of the fixed arm by bolts, a rectangular block is arranged at the left end of the cantilever, two parallel longitudinal bolt holes are arranged in the rectangular block, a connecting seat is arranged in front of the rectangular block, the connecting seat is fixed in front of the rectangular block, a pair of rollers and two guide rods are arranged at the left end of the connecting seat, and the hook arm is also provided with a clamping wheel for fixing the cantilever. The principle block diagram of the controller is shown in Figure 1.

　　When the textile machine is operating normally, the adjustment clutch is in a reliable separation state under the control of the single-chip computer PIC16F874. When the machine needs to be restarted after being shut down for some reason, press the adjustment button, and the system sends an adjustment signal to make the adjustment clutch control circuit work, and the adjustment clutch is in an engaged state. At this time, the adjustment motor rotates forward, reverse, forward and reverse, and counter-rotate under the control of the system, and adjusts the tightness of the weft to make it appropriately dense. After the adjustment is completed, the adjustment clutch returns to the separation state and displays the end signal of the tension adjustment.

　　2 Hardware Circuit Design

　　According to the function of the system, reliable control is the premise and accuracy is the key. The hardware strives to have a simple structure to improve reliability, while accuracy is guaranteed by precise speed change mechanism and detection circuit. Part of the hardware circuit is shown in Figure 2.

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　　2.1 MCU Selection

　　Since the system requires high adjustment accuracy, it is easy to set the adjustment amount and can protect against power failure. PIC16F874 contains 10b A/D conversion, high speed and low price. It has 128B electrically erasable E2PROM memory, which can easily write the adjustment amount for later use. 16F874 also has a watchdog to ensure the reliability of system program operation. At the same time, the synchronous serial module (SSP) lays the foundation for networking with industrial computers in the future.

　　2.2 Detection Circuit

　　The detection part mainly completes the detection of the clutch state and textile machine, and uses a photoelectric encoder to improve the detection accuracy. In order to ensure the safety of the MCU, all detection signals are connected to the MCU through an optical coupler. The circuit is shown in Figure 2.

　　2.3 Adjustment amount setting and display

　　In order to improve the adjustment accuracy, the following measures are taken: adopting a precise gear reduction mechanism; increasing the operating frequency of PIC16F74 to 20 MHz, and the execution time of an instruction is only 1μs, thereby improving the adjustment accuracy. As shown in Figure 3. RD0~RD6 of the microcontroller is used as the digital tube segment selection signal, RE0~RE2 is used as the digital tube chip selection signal, DS1 is used to display forward, reverse, forward and reverse, and reverse; DS2, DS3 display the set adjustment amount.

　　2.4 Control Circuit

　　The control of the system includes main motor locking, clutch motor, and adjustment motor. They are controlled by the output of the single-chip I/O ports RA0, RA1, RA2, and RA3. In order to ensure the safety of the single-chip, all output control signals are isolated by optical coupling, amplified by transistors, and driven by control relays and field effect transistors, so that the textile machine can achieve fast and reliable control.

　　3 Software Design

　　In the software design, a modular structure is adopted. The whole program consists of the main program and various functional subroutines and interrupt service programs. The system software flow chart is shown in Figure 4, which mainly includes initialization adjustment amount setting, display, detection and control of the working state of the clutch, and adjustment of the motor working state control.

　　The system has a simple structure, stable and reliable operation, high control accuracy, perfect protection function, and leaves certain resources for future technical improvements. It is low-cost and has received good feedback from users. It has laid a solid foundation for the future mechanical textile industry, allowing the speed of textile production to increase and the efficiency of production to be accelerated.

References:

[1]. PIC16F874 datasheet http://www.dzsc.com/datasheet/PIC16F874_4.html.
[2]. PIC16F74 datasheet http://www.dzsc.com/datasheet/PIC16F74_861.html.
[3]. DS1 datasheet http://www.dzsc.com/datasheet/DS1_1106249.html.