Abstract: The mechanical let-off mechanism of the SAURER400 loom imported from Switzerland is improved by using a 110BF003 stepper motor. The mechanism design and motor control method are presented . Experimental results show that the stepper motor let-off device is superior to the mechanical let-off mechanism, is more sensitive to tension fluctuations, reduces the density of the warp, reduces the number of warp breaks, is easier to operate, and has lower cost, making it worthy of widespread application. Keywords : stepper motor; electronic let-off; SAURER400 loom; control method The system is easier to operate and more economical. It can be used for reference. Key words: stepping motor; electronic let-off system; SAURER400 loom; controlling method. Currently, many shuttleless looms in China still use mechanical let-off mechanisms. Their disadvantages include: large processing errors and mechanical wear, low control precision; gear replacement is required when modifying weaving parameters such as weft density, making operation inconvenient and the mechanism complex; poor dynamic response at high speeds; and difficulty in adjusting warp tension. Therefore, many textile mills need to upgrade their existing mechanical let-off looms. This paper uses a stepper motor to upgrade the electronic let-off mechanism of a SAUR2ER400 rigid rapier loom imported from Switzerland that uses a mechanical let-off mechanism. A microcontroller is used to control the stepper motor, and the motor frequency is controlled by the microcontroller's timer T1. The pulse width is changed by varying the timing duration. The acceleration and deceleration of the motor are achieved by making the initial value of T1 change at a constant speed. The effectiveness of this improved mechanism was tested through experiments. 1. Selection of Stepper Motor In traditional electronic warp feeding systems, AC/DC servo motors are generally used. DC servo motors have a large linear speed range, are easy to control, and have high efficiency, but the electrical sparks generated by the brushes will interfere with the normal operation of the control system and pose safety hazards. AC servo motors have good low-speed performance and are resistant to electromagnetic interference, but their mechanical characteristics are relatively soft, their linear speed range is small, and the frequency converters used to match them are relatively expensive. In comparison, stepper motors have the characteristics of flexible and diverse functions, accurate pulse output, strong real-time performance, and good high-frequency characteristics. Through software design, various complex controls can be achieved, and their system cost is low, but their torque is relatively small. During the weaving process, when the warp feed motor rotates forward, causing the warp beam to feed the warp yarns, the warp tension is not a load resistance but a driving force. The stepper motor only needs to output a small torque to feed the warp yarns. When the warp feed motor rotates in reverse to tension the warp yarns, the warp tension becomes a load resistance, and the stepper motor needs to output a larger driving torque. This design uses a reactive stepper motor 110BF003 with a starting frequency of 1500 Hz and an operating frequency of 7000 Hz. Its torque characteristics are shown in Figure 1. According to the torque-frequency characteristic curve, the torque drops sharply when the motor frequency reaches a certain level. During warp feeding, there is a time constraint, and the motor frequency requirement is relatively high, which is exactly when the motor torque requirement is not high. However, when the motor rotates in reverse to tension the warp yarns, there is no time constraint, and the frequency can be reduced to meet the motor torque requirement. The reactive stepper motor 110BF003 can meet the warp feeding requirements, and the motor and driver are relatively inexpensive, resulting in a high cost-performance ratio. 2 Improvement of the Warp Beam Drive System 2.1 The SAURER400 mechanical warp feed mechanism is used in SAURER400 looms. Power is transmitted from the main motor through belts and gears. A simplified diagram of the mechanism is shown in Figure 2. When the reed seat foot drives the swing arm to swing up and down via the transmission, the overrunning clutch ring also swings, causing the inner and outer rings of the overrunning clutch to rotate together. Since the ratchet and clutch are connected by screws, the pawl drives the ratchet to rotate in the same direction as the clutch. A coaxial worm drives the worm wheel, and the warp feed gear, coaxial with the worm wheel, meshes with the warp beam side plate gear, finally driving the warp beam to rotate and feed out the corresponding length of warp yarn. 2.2 Improved Mechanism A simplified diagram of the improved electronic warp feed mechanism is shown in Figure 3. The mechanical transmission linkage is disconnected, and a separate stepper motor is used as the warp feed motor to drive this device. As shown in the simplified diagram, the motor drives gear 3 to mesh with gear 2 through a reducer, and then directly transmits the power to the worm gear and worm wheel coaxial with gear 2. This power is then transmitted to the warp feed gear, which meshes with the warp beam side plate gear, ultimately driving the warp beam to rotate and achieve the purpose of warp feeding. The reducer, gears 2 and 3, and the worm gear and worm wheel all contribute to the speed reduction of the motor. 3. Stepper Motor Speed ​​Control 3.1 Stepper Motor Speed ​​Calculation Assuming the warp diameter is D and the weft density in the fabric specification is Pw, the required warp feed per weft is [sup][ 5 ][/sup]: The number of steps the motor needs to run per revolution of the main shaft is: Where n1[sub]max[/sub] is the maximum number of pulses of the motor; n1[sub]min[/sub] is the minimum number of pulses of the motor. At this time, the motor frequency is very high, greater than the starting frequency, and cannot be directly used for uniform speed operation; there is an acceleration and deceleration problem. 3.2 Motor Acceleration and Deceleration Control Motor acceleration and deceleration control refers to the process of a stepper motor going through several stages: starting, accelerating, constant speed, deceleration, and stopping. Therefore, the operating frequency of a stepper motor is constantly changing. During the starting and acceleration process, the operating frequency of the stepper motor gradually increases to the running frequency. It is important to note that if the frequency increase is too rapid, the previous drive pulse may not be able to bring the motor rotor into the dynamic stable zone of the next pulse, resulting in step loss. However, if the frequency increase is too slow, the motor's acceleration time will be too long, which may not meet the requirements of certain processes. Currently, the main methods for stepper motor acceleration and deceleration control at home and abroad are linear acceleration/deceleration speed curves and exponential acceleration/deceleration speed curves. This design uses a timer inside a microcontroller to send stepper motor pulses. After each timer interrupt, the timing constant is changed, so that the pulse frequency gradually increases during acceleration and gradually decreases during deceleration. If an exponential acceleration/deceleration curve is used to control acceleration and deceleration, an initial value table for the microcontroller's timer needs to be prepared in advance, which involves a large amount of calculation and is quite troublesome. Therefore, this experiment uses a single-chip microcomputer-based linear acceleration/deceleration, which is between linear and exponential acceleration/deceleration, as shown in Figure 4. In the figure, f[sub]o[/sub] is the starting frequency, f[sub]h[/sub] is the frequency during constant speed, and t[sub]h[/sub] is the end time of each cycle. Since the single-chip microcomputer counter is an incrementing counter, and the stepper motor speed changes in a curve, close to a curve, this method is simple to program and has better performance than linear acceleration/deceleration control. In the design, timer T1 is used to generate motor pulses. When the timer expires, a pulse is sent from the single-chip microcomputer P1.0 port, and the motor moves one step. During acceleration and deceleration, each step is 4 steps, and the difference in the initial value of the timer between two adjacent steps is 16. Its flowchart is shown in Figure 5. 3.3 Pulse Count Adjustment This design uses incremental PID control, but the motor operation is in units of steps. The data obtained from PID calculation cannot be directly used to adjust the number of steps of motor operation, and a certain comparison and judgment are required. Within one revolution of the loom, A The /D parameter samples the tension value 8 times. The microcontroller obtains these data and averages them to obtain the tension value for this week. This value is compared with the set standard tension value. The difference is calculated using PID control. After certain comparisons and judgments, the number of steps the motor needs to run next week can be determined. The flowchart of the program to calculate the number of pulses the motor needs to send next week is shown in Figure 6. [align=center] Figure 5 T1 interrupt flowchart[/align] After the same number of pulses n times, this number of pulses is adjusted to the pulse base. The number of pulses is then adjusted based on this base. n is the number of adjustments, and the number of pulses adjusted is the adjustment number. Initially, the number of adjustments is set to 10. The data obtained from the PID calculation is placed in two bytes. First, the high byte is compared. If the high byte is greater than zero, the number of adjustments is changed to 3. At the same time, if the tension for this week is outside the range, the adjustment number is set to 4, otherwise it is set to 8. If the high byte is less than zero, the low byte is compared. If it is greater than BAH, the adjustment number is set to 4. If it is less than BAH but greater than 46H, the adjustment number is set to 2. P If the ID calculation result is positive, the pulse base number is added to the adjustment number to obtain the motor pulse number for the next week; if it is negative, it is subtracted. If the tension exceeds the range this week, the pulse change rate is slowed down, i.e., the adjustment number becomes 6. The pulse base number is determined based on the adjustment number. [align=center] Figure 6 Flowchart of Motor Pulse Number Adjustment[/align] 4 Experimental Results A large number of experiments were conducted on the improved mechanism. Due to the influence of the five major movements of the loom, the tension fluctuates within a cycle. The tension value is measured by a sensor, amplified by an amplifier, and outputs a voltage of 0-5V. This voltage is proportional to the pressure value. After A/D sampling, it is sent to the microcontroller, which processes the data and calculates the number of pulses the motor needs to send. In the experiment, the loom was first allowed to use the mechanical warp feeding mechanism to sample the tension value, and the obtained tension value was used as the standard tension value of the fabric for this experiment. The initial number of motor steps was calculated based on the previous theory. Based on this, the actual number of motor steps needed was adjusted by adjusting the tension. The experimentally obtained number of motor steps needed was not significantly different from the theoretically calculated value. Table 1 shows a comparison between the theoretical values ​​and the improved warp feed base values. The number of motor steps is determined by the number of pulses; one pulse corresponds to one motor step, and the pulse number can only be an integer. Experiments show that the improved mechanism enables the loom to weave normally and ensures that the tension fluctuates within the range of 343–378 N. The improved mechanism allows the motor to reverse even when the tension value is 490 N, and the adjustment time can be controlled within 8 cycles. [align=center]Table 1 Comparison of Theoretical and Experimental Warp Feed Base Values ​​of the Improved Mechanism[/align] Under the conditions of a temperature of 28 ℃, humidity of 650/0, spindle speed of 390 r/min, and fabric types of 58.3 × 58.3 tex, 200 × 200 threads/10 cm, and 160 cm wool-polyester plain weave, tests were conducted using both mechanical warp feed and the improved system. The test results are shown in Table 2. [align=center]Table 2 Comparison of Two Warp Feed Methods[/align] 5 Conclusion (1) Stepper motors can be used in the electronic warp feeding transformation of SAURER400 looms and can give full play to the advantages of stepper motors. The speed control is convenient, the real-time performance is good, and the cost is low. (2) Only some changes are made to the original mechanical warp feeding mechanism to make the stepper motor drive the warp beam to rotate and become electronic warp feeding. This method is simpler and more adaptable than the mechanical method. When changing the fabric, only the parameters need to be set and the program can be automatically adjusted without changing the mechanical structure. (3) The improved electronic warp feeding device is more sensitive to tension control, has good control of density and sparseness, and has a lower breakage rate. (4) Experiments show that the system is easy to operate, has low cost, and has promotional value for the transformation of old machines and the matching of new machines. References: [1] Mao Xinhua. Textile Technology and Equipment [M]. Beijing: China Textile Press, 2004. [2] Zhou Junyan, Xiao Qiang. Design of Electronic Warp Feeding and Take-up Control System Based on Single-Chip Microcomputer [J]. Computer Measurement and Control, 2005, 13 (7): 698 - 700. [3] Zhou Qihong, He Yongyi, Guo Shuai. Intelligent electronic warp feed control system based on DSP [J] 1 Mechatronics, 2003, (6): 59 - 62. [4] Chen Ge, Mao Limin, Lin Shen. Design of electronic warp feed weaving beam drive system [J]. Journal of Donghua University: Natural Science Edition, 2005, 31 (6): 66 - 69. [5] Yang Jiancheng, Jiang Xiuming. Improved design of warp feed mechanism for SAURER400 loom [J] 1 Journal of Tianjin University of Technology, 2006, 25 (5): 55 - 57. [6] Liu Xiangdong, Wang Shudong, Wang Guilian. Research on acceleration and deceleration motion of stepper motor for punch press [J] 1 Journal of Jiamusi University: Natural Science Edition, 2005, 23 (4) : 577 - 578.