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Three dimensional field analysis of two-phase hybrid linear stepping motor

Abstract: as an ideal high-tech linear driver, two-phase hybrid linear stepping motor has been widely used in high-resolution direct drive linear servo system. This paper takes the SLPMU-025A produced by Japan Kobelco Electric Co., Ltd. as the research prototype, uses the Maxwell 3D software of Ansoft company to establish the three-dimensional model of SLPMU-025A, calculates the static magnetic field of the motor through the finite element method, and focuses on the analysis of the magnetic field Bayer compensation scale in the tooth layer area of the motor, which greatly improves the calculation accuracy. The static thrust displacement characteristics of the motor are obtained

key words: linear stepping motor; Finite element analysis; Three dimensional magnetic field

1 Introduction to SLPMU-025A

slpmu series linear stepper motor is a two-phase linear stepper motor developed and produced by Kobelco Electric Co., Ltd. SLPMU-025A was developed and designed as an early product of thin printer at the end of microcomputer. Figure 1 shows its appearance

Figure 1 appearance of SLPMU-025A

the structure of SLPMU-025A is shown in Figure 2, figure 3 and Figure 4. It is composed of a mover and a stator. When energized in a certain way, the mover makes a step-by-step linear motion above the stator. The back iron, permanent magnet, iron core and winding are combined to form the mover of the motor. The iron core of the mover is made of silicon steel sheets. The iron core column surrounded by the coil forms the magnetic pole of the motor, which is arranged in front and back rows. Three teeth are evenly arranged on each magnetic pole

Fig. 2 front view of SLPMU-025A Fig. 3 side view of SLPMU-025A

the stator of the motor is made of silicon iron sheets carved into two rows of grid shape and pasted on soft iron (as shown in Fig. 4). The tooth width and slot width on the magnetic pole are equal to those on the stator, and the tooth pitch is equal

Figure 4 top view of SLPMU-025A stator

during single-phase 4-beat operation, that is, when the motor is powered on in sequence, the actuator of the motor will τ/4 steps to the right. The difference between the front and rear rows of teeth of the stator τ/2（ τ Is a tooth pitch), which can make the rotor of the motor run more smoothly. The magnetic poles corresponding to the rear teeth of the stator along the y-axis direction are in turn

2. The three experimental equipment of SLPMU-025A that do not meet the requirements of these verification regulations are dimensional magnetic field analysis that is not allowed to be put into use

2.1 Establish a three-dimensional simulation model

use Maxwell 3D to analyze the three-dimensional magnetic field of SLPMU-025A. First, establish its three-dimensional simulation model, see Figure 5

because the static characteristic analysis is needed, the moving range of the mover on the stator is limited, so the stator only takes a small section, which can greatly reduce the amount of subdivision calculation and shorten the calculation time. After establishing the three-dimensional model, define the properties of each material, then define the boundary conditions and source current, and finally calculate the force. First calculate the electromagnetic force on SLPMU-025A at a fixed point, and then you can see the corresponding sectional drawing and magnetic field analysis through post-processing. First of all, take the point when the rotor teeth and stator teeth of pole a are aligned as an example to do its electromagnetic force calculation and magnetic field analysis. The result is that the electromagnetic force on the mover in the Y direction is 19.121 [n], and the number of triangular prism dividing units reaches 165061

2.2. The magnetic field distribution in the back iron

the calculation results of the magnetic field distribution of the back iron part corresponding to the mover are shown in Figure 6. It can be seen from Figure 6 that the magnetic field distribution along the X axis is uneven, but it is considered to be the same in the two-dimensional magnetic field analysis

Fig. 6 magnetic density of the back iron corresponding to the mover

it can be seen from Fig. 6 that the maximum magnetic density of the back iron is 1.7949 [t], and there is no oversaturation. For the magnetic density calculation of two-phase hybrid linear stepping motor, the most critical part should be the tooth layer area

2.3. Analysis of the magnetic field in the tooth layer area

for the static characteristics of stepping motor, an important problem is to analyze the magnetic field in its tooth layer area. Since the stator teeth of SLPMU-025A are only 0.3mm high and 0.8mm wide, they are easily saturated. Fig. 7 and Fig. 8 show the stator surface magnetic density diagram obtained when the rotor a pole is tooth to tooth with the stator tooth, and the forward current is connected to B. The magnetic density of stator teeth corresponding to pole a and pole is shown in Figure 7. The magnetic density of stator teeth corresponding to b-pole and A-pole is shown in Figure 8. It can be seen from Figure 7 that the magnetic density under pole a is greater than that under pole B, because the relationship between pole a and stator is tooth to tooth, while the relationship between pole a and stator is tooth to slot, and the magnetic flux is always closed along the path of maximum magnetic conductivity. It can be seen from figure 8 that the maximum magnetic density under pole B reaches 3.4295 [t], and oversaturation occurs. Due to the mutual cancellation of magnetic flux under the A-pole, the magnetic density is very small, and the maximum is only 0.6956 [t]

3. Comparison between the experimental value and the calculated value of the static thrust displacement characteristic of SLPMU-025A

when the single-phase coil of SLPMU-025A is continuously energized with 1.2A DC, the comparison between the calculated value and the experimental value of the static thrust displacement characteristic of one cycle is shown in Figure 9

Fig. 9 Comparison between experimental and calculated values of SLPMU-025A static thrust displacement characteristics

according to the structure of SLPMU-025A, a two-phase hybrid linear stepper motor, which obtains mineral resources by holding shares, its static thrust is only related to the relative position of the mover and stator, and should be cyclical and symmetrical up and down. The absolute values of the maximum positive and minimum negative static thrust should be equal. It can be seen from Figure 9 that the calculated value of the static thrust displacement characteristic of SLPMU-025A is similar to the overall trend of the experimental value, and the calculated value of the upper half is roughly consistent with the experimental value. The main reason for the difference between the calculated value and the experimental value in the off-duty part is that the influence of friction is ignored and the problem of frequent applause may occur in the later stage, which is the main reason for the large deviation between the experimental value and the calculated value in the negative direction

4. Conclusion

in this paper, the static magnetic field in the motor is calculated by using the finite element software Maxwell 3D, with emphasis on the analysis and calculation of the magnetic field changes in the tooth layer area of the motor. The static thrust displacement characteristics of the motor are obtained and compared with the experimental values

in this paper, the "field" method is used to replace the previous "path" method and the "field circuit combination" method, which greatly improves the calculation accuracy, especially for the accurate solution of the magnetic field in the tooth layer area, which is the key part of the stepping motor. For example, the material can be selected accurately according to the saturation degree of the magnetic density. This paper mainly analyzes the static field of stepping motor, and on this basis, further in-depth calculations such as transient calculations can be carried out

References:

1 Ding Zhigang The principle, control and application of linear stepping motor Beijing: China Machine Press, 1994

2 Niu Hua Research on two phase hybrid linear stepping motor Taiyuan: [Master's Thesis] Taiyuan University of technology, 2000,4 (end)

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