Abstract: This paper studies the speed measurement method of brushless DC motors in high-speed industrial flatbed sewing machines with a wide speed range. The principles and implementation of the pulse counting method and the pulse period method are analyzed, along with the relationship between measurement accuracy and speed. Different speed measurement methods are proposed for different speed ranges to ensure high-accuracy speed parameters throughout the entire speed range. Practical application results show that the proposed speed measurement method effectively meets the response time and accuracy requirements of the control law for high-speed industrial flatbed sewing machines. Keywords: brushless DC motor; high-speed industrial flat sewing machine; speed measurement; wide-range speed regulation [b][align=center]Rotative Speed ​​Measurement Methods Researching for high-speed wide-range Flat sewing machine[/align][/b] JIANG Jian-kui LIU Jian-chen Abstract: The rotative speed measurement methods of high-speed wide-range flat sewing machine brushless DC motor are discussed. The Pulse numeration method and pulse period method are introduced in this paper. The precision of these two methods and the relationship between precision and rotative speed are analyzed. Based on the analysis, a compounding method suitable for the whole speed range with higher precision is advanced. The application shows that the compounding method has achieved the precision and response time of the control rule. Key words: brushless DC motor, high-speed flat sewing machine, speed measurement, wide-range-timing 0 Introduction With the development of the sewing industry in recent years, high-speed industrial flat sewing machines, with their high degree of automation, simple operation, and ability to significantly improve sewing efficiency, are gradually replacing traditional mechanical sewing machines. Currently, China has a huge demand for industrial sewing machines. The main technical challenge of high-speed industrial flatbed sewing machines lies in rapid and precise needle-stopping control. Due to the special nature of the sewing process, it is generally required to stop the needle within 3 revolutions within a speed range of 300-8000 r/min, with a stopping accuracy within 5mm. This places high demands on the needle-stopping control algorithm, thus requiring high accuracy in the speed parameters provided to the control algorithm. This design requires a speed measurement error of no more than 0.5%. 1. Speed ​​Measurement of Brushless DC Motors There are many methods for speed measurement, such as Hall effect speed sensors, tachogenerators, photoelectric speed sensors, inductive speed sensors, and rotary transformer speed sensors. In industrial flatbed sewing machines, incremental photoelectric encoders are commonly used. They can not only detect the motor's speed but also determine its direction of motion. The working principle of an incremental photoelectric encoder is as follows: a certain number of photoelectric holes are evenly distributed on the scale. When light passes through the photoelectric holes, the photosensitive sensor generates a logic "1" signal; when the light-emitting diode is blocked, the photosensitive sensor generates a logic "0" signal. Thus, the two photosensitive sensors will generate two orthogonal signals A and B with a phase difference of 90° [1][2]. The speed of the sewing machine can be calculated by detecting the pulses output by the photoelectric encoder. By selecting different photoelectric encoders, the motor can generate different numbers of pulse signals in one rotation. Here, it is assumed that the number of pulses generated by the motor in one rotation is N[sub]0[/sub], and the speed can be calculated using two algorithms [3]. 1.1 Pulse counting method: The position pulse signal is counted per unit time to obtain the rotation angle per unit time to calculate the speed. If the time interval is the sampling time T[sub]s[/sub], and the number of pulses measured is M, then the measured speed is: (1) Calculated. The sampling period T[sub]s[/sub] is determined by the performance of the control system. Then the speed n is proportional to the number of pulses per unit time. The measurement of speed by the pulse counting method can be completed by the following software process, where M is obtained by the difference between two samples, that is, the value of M at time is where is the position signal used at time. The specific implementation will be described later in the paper. 1.2 Pulse period method measures the time of one cycle of position signal to obtain the time of fixed angle to calculate speed. The time measurement can be obtained by counting the clock of microprocessor. If the clock frequency of microprocessor is f[sub]0[/sub] and the number of clocks counted in one cycle of position pulse signal is m, the speed to be tested can be calculated by (2). When the clock of microprocessor f[sub]0[/sub] and the number of pulses N[sub]0[/sub] are determined, the rotational speed n is inversely proportional to the number of clocks m in the pulse period. The pulse period measurement method can use the signal A or B of photoelectric encoder to generate an external interrupt to the timer of microprocessor to measure the width of the pulse, and then calculate the rotational speed by formula (2). 1.3 Implementation of two measurement methods In the hardware design of high-speed industrial flat sewing machine, LPC2138 based on ARM7 core is selected as the main controller. Using the external capture function of LPC2138, the speed can be calculated by software programming by capturing the pulse signal of photoelectric encoder[5]. The LPC2138's clock frequency can be configured via software; this design uses a 12MHz clock frequency. It's important to note that to ensure circuit reliability, the photoelectric encoder's pulse signal should ideally be isolated by a high-speed optocoupler before being connected to the LPC2138's capture pin. For the pulse counting method, a timer interrupt is used, and the number of captured photoelectric encoder pulses is read in the interrupt handler. The speed can be calculated using equation (1). For the pulse period method, the photoelectric encoder's pulse signal triggers a processor interrupt. The timer register value is read in the corresponding interrupt handler, and the speed can be calculated using equation (2). 2. Accuracy Analysis of the Two Measurement Methods In a DC brushless motor position detection system using an incremental photoelectric encoder disk, the accuracy of position measurement depends on the number of pulses output by the photoelectric encoder during one revolution of the motor. Common output pulse counts include 240, 720, and 1024. This design uses a photoelectric encoder with an output of 720. The accuracy of speed measurement is analyzed below. 2.1 Accuracy Analysis of Pulse Counting Measurement Method In speed measurement using the pulse counting method, the number of counted pulses M is related to the sampling period Ts and the position resolution N0. When the counted pulses change from M to M+1, according to Equation 1, the speed error of the pulse counting measurement method is: (3) The relative accuracy is (4) Obviously, to improve the relative measurement accuracy of the speed, a larger sampling period Ts or a higher position resolution can be used, and it is inversely proportional to the speed n of the motor. The speed regulation range of this system is 300 – 8000 r/min. The sampling period Ts in the design of the system control law is 5ms. The measurement accuracy at various speeds can be calculated and shown in Table 1. The data in the table are percentages. Table 1 Measurement accuracy of pulse counting method at various speeds The data in Table 1 show that the pulse counting method has higher accuracy in the high speed range. This method is suitable for high-speed operation of motors. 2.2 Accuracy Analysis of Pulse Period Measurement Method The pulse period method counts the pulses by the processor clock. The count pulse m is related to the clock frequency f[sub]0[/sub] and the position resolution N[sub]0[/sub]. When the count pulse changes from m to m+1, according to equation (2), the error of the pulse measurement method is (5). The relative speed accuracy is (6). When the microprocessor clock is f[sub]0[/sub]=12MHZ, the measurement accuracy at various speeds can be calculated according to equation (6). See Table 2. The data in the table are percentages. Table 2 Measurement accuracy of pulse period method at various speeds. From the data table, it can be seen that the measurement accuracy of pulse period method is high in the low speed range of motor, but poor in the high speed range. At the same time, in practical applications, when using pulse period measurement method, the output pulse of photoelectric encoder causes the processor to be interrupted. If this method is used in the high speed stage, it will cause the processor to be interrupted frequently, which will consume a lot of processor time. 3 High-speed industrial flat sewing machine speed measurement method According to the above accuracy analysis, pulse counting method is used in the high speed range, while pulse period method is suitable for low speed. For speed control systems with a large speed range, it is difficult to guarantee high speed measurement accuracy across the entire speed range using any of the above speed measurement methods. Only by combining the two methods can a more ideal result be obtained. 3.1 Combined Speed ​​Measurement Method Substituting N[sub]0[/sub]=720 into equations (4) and (6), the "accuracy/speed (S/n)" curve in Figure 1 is plotted. In the figure, S represents accuracy, expressed as a percentage, and n represents speed. The intersection of the two curves in the figure is S[sub]0[/sub]=0.4074, and the speed is n[sub]0[/sub]=4091 r/min. [align=center] Figure 1 Curves of speed n and accuracy S for two speed measurement methods[/align] This indicates that when n>n[sub]0[/sub], the speed measurement accuracy of the pulse counting method can be higher than 0.4074%, while when n 4 Conclusions Due to the need for precise needle stop control, the speed measurement accuracy of high-speed industrial flat sewing machines is required to be high. The speed measurement method proposed in this paper for high-speed industrial flat sewing machines has been verified by practice and proved to be correct and accurate. It can ensure that the speed measurement error is less than 0.5%, which meets the requirements of the system control law. References [1]. Li Weimin, Jiang Man. Speed ​​feedback and control counting based on photoelectric encoder [J]. Modern Electronics Technology, 2004 (23). [2]. Jiang Qingmin. A high-precision speed measurement and acceleration measurement method based on photoelectric encoder [J]. Microcomputer Information, 2004 [3]. Dong Yunxiang, Liu Yujie. Research on speed measurement method of high-speed wide-range speed-regulating motor for aviation [J]. Computer Measurement and Control, 2005.13 (2) [4]. Zhang Chen. Principle and application of DC brushless motor [M]. Beijing: Machinery Industry Press, 2001 [5]. LPC2131/2132/2138 User Manual. Philips Semiconductors 2004