Rotor structure of built-in high-speed motorized spindle motor of numerical control machine tool and design method thereof

Abstract

The invention relates to a rotor structure of a built-in high-speed motorized spindle motor of a numerical control machine tool and a design method. The design method comprises the following steps: determining an initial structure of a rotor of the motorized spindle motor as a uniform circumferential outer contour; the outer contour of the rotor is changed, and the uniform circumferential outer contour is changed into a non-uniform circumferential outer contour composed of arcs with different circle centers; an auxiliary groove is additionally formed in the permanent magnet cavity; and by taking the average torque and the torque fluctuation as constraint conditions and taking the maximum iron loss as an optimization target, the size of the electric spindle motor rotor is optimized. The rotor structure can effectively reduce the iron loss of the electric spindle motor, thereby improving the heat dissipation of the motor, and improving the operation stability and reliability of the motor.

Description

Technical Field

[0001] The invention belongs to the field of motor optimization design, and in particular relates to a rotor structure of a built-in high-speed electric spindle motor for a numerically controlled machine tool and a design method thereof. Background Art

[0002] The spindle drive system is a key component of CNC machine tools. The electric spindle has been widely used in CNC machine tools due to its advantages in structure and performance. The spindle motor, as the core of the electric spindle drive system, provides power for the cutting, milling, boring, drilling and other operations of CNC machine tools. Its type selection, design and parameter optimization are very important for improving the performance and precision of the spindle drive system.

[0003] The permanent magnet of the built-in high-speed electric spindle motor is located inside the rotor, and a magnetic circuit is formed between the permanent magnet and the motor air gap. Therefore, the magnetic circuits of the motor d-axis and q-axis are different, and there is a magnetic resistance torque. When the electric spindle motor rotates at a high speed, the fundamental wave of the motor magnetic field and the harmonic alternating frequency caused by the non-sinusoidal distribution of the permanent magnet and the rotor magnetomotive force also increase, resulting in a large iron loss in the stator and rotor of the motor, reducing the motor efficiency. When the rotor heat dissipation conditions are poor, the excessive rotor iron loss will also increase the risk of irreversible demagnetization of the permanent magnet, reduce the reliability of the motor, and affect the processing performance of the CNC machine tool. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a rotor structure of a high-speed electric spindle motor installed in a CNC machine tool and a design method thereof. By improving the rotor topology of the motor and optimizing the magnetic circuit, the harmonic content in the magnetic field can be reduced, thereby reducing the iron loss of the motor, improving the motor efficiency, reducing the risk of irreversible demagnetization of the permanent magnet, and improving the operating reliability of the electric spindle motor and the CNC machine tool.

[0005] The technical solution of the present invention is: a rotor structure of a built-in high-speed electric spindle motor for a CNC machine tool, including a plurality of permanent magnet cavities arranged in pairs along the circumferential contour of the rotor, the motor is a built-in permanent magnet synchronous motor, the two permanent magnet cavities arranged in pairs are distributed in a "V" shape, and the outer contour of the rotor is an uneven circular outer contour composed of arcs with different centers; a trapezoidal auxiliary groove is added at a position obliquely above the permanent magnet cavity on one side close to the outer contour of the rotor and at the edge of the permanent magnet cavity.

[0006] The present invention also provides a rotor structure design method, comprising:

[0007] Step (1) The electric spindle motor is a built-in permanent magnet synchronous motor, and the permanent magnet cavity adopts a "V" shape distribution;

[0008] Step (2) determining that the initial structure of the rotor of the electric spindle motor is a uniform circular outer contour;

[0009] Step (3) changing the outer contour of the rotor, changing the uniform circular outer contour into an uneven circular outer contour composed of circular arcs with different centers;

[0010] Step (4) adding an auxiliary slot at the permanent magnet cavity;

[0011] Step (5) optimizes the changed uneven rotor size to reduce the iron loss of the electric spindle motor.

[0012] The present invention has the following beneficial technical effects: a rotor structure and a design method for a high-speed electric spindle motor installed in a CNC machine tool are proposed, which can more efficiently optimize the motor magnetic circuit and reduce the harmonic content in the magnetic field, thereby reducing the motor iron loss, improving the motor efficiency, reducing the risk of irreversible demagnetization of permanent magnets, and improving the operating reliability of the electric spindle motor and the CNC machine tool. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is the initial structure diagram of the electric spindle motor rotor;

[0014] Figure 2 The structure diagram of the rotor of the electric spindle motor after the outer contour of the rotor is changed;

[0015] Figure 3 This is a schematic diagram of the rotor structure after adding auxiliary slots in the permanent magnet cavity.

[0016] Figure 4 Schematic diagram of optimized variables for the rotor;

[0017] In the figure, 1 is a uniform circular outer contour, 2 is a permanent magnet cavity, 3 is a non-uniform circular outer contour, and 4 is an auxiliary groove. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above-mentioned purpose, the present invention adopts the following technical scheme.

[0019] The present invention proposes a rotor structure of a high-speed electric spindle motor built into a CNC machine tool, such as Figure 2 (a), (b), Figure 3As shown in (a) and (b), it includes a plurality of permanent magnet cavities 2 arranged in pairs along the circumferential contour of the rotor, and the two permanent magnet cavities 2 arranged in pairs are distributed in a "V" shape; the outer contour of the rotor is composed of an uneven circumferential outer contour 3 composed of arcs with different centers; the uneven circumferential outer contour 3 is obtained by changing the uniform circumferential outer contour 1, and an auxiliary groove 4 is added at the permanent magnet cavity 2.

[0020] The uneven circumferential outer contour 3 of the rotor is specifically as follows: Figure 2 (a), (b), Figure 4 As shown in (a) and (b), the initial structure of the rotor is a uniform circular outer contour 1, O is the center of the uniform circular outer contour 1, and the arc portion corresponding to the two "V"-shaped permanent magnet cavities 2 arranged in pairs is taken. The "V"-shaped permanent magnet cavities 2 are set to N pairs, and the degree of the arc portion corresponding to each pair of "V"-shaped permanent magnet cavities 2 is , so that the radius of the rotor air gap and the position of the permanent magnet cavity 2 remain unchanged, that is, |OR1|=|OO'|+|O'R1|, where R1 is the intersection of the midline of a pair of "V"-shaped distributed permanent magnet cavities 2 and the outer contour of the rotor, O' is the changed center of the circle, and an arc is drawn with the changed O' as the center and O'R1 as the radius. R1 is the midpoint of the arc, P1 and P2 are the two end points of the arc, that is, the one-N outer contour P1P2 of the uneven circular outer contour 3 is obtained, P1 and P2 are the vertices at both ends of the arc respectively, and the one-N outer contour is arrayed along the circumference, that is, the uneven circular outer contour 3 composed of arcs with different centers is obtained.

[0021] like Figure 3 As shown, a trapezoidal auxiliary groove is added at the upper side of the permanent magnet cavity 2 close to the outer contour of the rotor and at the edge of the permanent magnet cavity 2.

[0022] The distance of the center O' of the uneven circumferential outer contour 3 from the center O, the distance of the auxiliary slot 4 from the rotor outer contour and the slotting distance of the auxiliary slot are set so that the iron loss of the electric spindle motor is minimized.

[0023] The present invention also proposes a rotor structure design method for a built-in high-speed electric spindle motor of a numerically controlled machine tool, comprising:

[0024] Step (1) The electric spindle motor is a built-in permanent magnet synchronous motor, and the permanent magnet cavity 2 adopts a "V" shape distribution;

[0025] Step (2) determining that the initial structure of the rotor of the electric spindle motor is a uniform circular outer contour 1;

[0026] Step (3) changing the uniform circular outer contour 1 to an uneven circular outer contour 3 composed of circular arcs with different centers;

[0027] Step (4) adding an auxiliary slot 4 at the permanent magnet cavity 2;

[0028] Step (5) optimizes the changed uneven rotor size to reduce the iron loss of the electric spindle motor.

[0029] The following takes a high-speed electric spindle motor installed in a CNC machine tool as an example to explain the implementation of the present invention in detail. The motor parameters are shown in Table 1.

[0030] Table 1 Motor parameters

[0031]

[0032] The initial structure diagram of the motor rotor is as follows: Figure 1 As shown, 1 is the uniform circular outer contour, and 2 is the permanent magnet cavity; Figure 2 (a) and (b) are the structural diagram and enlarged diagram of the electric spindle motor rotor structure after the rotor outer contour is changed. O is the center of the uniform circular outer contour 1, and O' is the center of the circle after the change. The arc portion corresponding to the two "V"-shaped permanent magnet cavities 2 arranged in pairs is taken. The "V"-shaped permanent magnet cavities 2 are set to N pairs, and the degree of the arc portion corresponding to each pair of "V"-shaped permanent magnet cavities 2 is , so that the radius of the rotor air gap and the position of the permanent magnet cavity 2 remain unchanged, that is, |OR1|=|OO'|+|O'R1|, where R1 is the intersection of the midline of a pair of "V"-shaped distributed permanent magnet cavities 2 and the outer contour of the rotor, O' is the changed center of the circle, and an arc is drawn with the changed O' as the center and O'R1 as the radius. R1 is the midpoint of the arc, P1 and P2 are the two end points of the arc, that is, the one-N outer contour P1P2 of the uneven circular outer contour 3 is obtained, P1 and P2 are the vertices at both ends of the arc respectively, and the one-N outer contour is arrayed along the circumference, that is, the uneven circular outer contour 3 composed of arcs with different centers is obtained.

[0033] like Figure 3 As shown in (a) and (b), a trapezoidal auxiliary groove 4 is added at the upper side of the permanent magnet cavity 2 close to the outer contour of the rotor and at the edge of the permanent magnet cavity 2;

[0034] Taking reducing the iron loss of the electric spindle motor as the optimization goal, the rotor structure is further optimized. Taking the one-eighth rotor structure diagram as an example, the selection of optimization variables is as follows: Figure 4 As shown:

[0035] A-the distance of the center O' of the uneven circular outer contour 3 from the center O; Figure 4 As shown in (a);

[0036] B-the distance between the auxiliary slot 4 and the outer contour of the rotor;

[0037] C- slotting distance of auxiliary slot 4; Figure 4 as shown in (b).

[0038] Based on the rotor structural parameters and processing requirements before motor optimization, the value ranges of optimization variables A, B, and C are determined. Among them, variable A will affect the unevenness of the rotor outer contour, and R2 is the intersection of the extension line of OP1 and the initial outer contour of the motor with point O as the center. That is, the larger A is, the larger |P1R2| is, the more uneven the rotor outer contour is, the smaller the rotor structural area is, and the average torque decreases accordingly. The smaller A is, the smaller |P1R2| is, and the higher the precision requirement for processing is. Therefore, after comprehensive consideration, the value range of A is determined to be 5mm to 8mm; variable B will affect the strength of the rotor structure. To ensure that the rotor does not deform during processing, the minimum value of variable B is 2mm. At the same time, in order to ensure that the auxiliary slot is utilized, the maximum value of B is 5mm; variable C affects the position of the auxiliary slot. According to the principle of the auxiliary slot changing the rotor magnetic circuit, the slot position should be located obliquely above the side of the permanent magnet cavity close to the rotor outer contour and close to the edge of the permanent magnet. Therefore, the maximum value of C is determined to be 6mm. When the value of C is small, it is impossible to leave enough space for the auxiliary slot. Therefore, the minimum value of C is 3mm. According to the above analysis, an optimization variable value table is established, as shown in Table 2;

[0039] Table 2 Optimization variable value table

[0040]

[0041] According to the variable value range shown in Table 2, the parametric scanning test design of the rotor structure is carried out in the finite element analysis software;

[0042] Calculate the electromagnetic performance of the electric spindle motor in each group of tests, and record the maximum iron loss, average torque and torque fluctuation results of each group of tests;

[0043] With the constraints that the average torque is greater than or equal to the rated torque of the electric spindle motor 100Nm and the torque fluctuation is less than or equal to 4%, the test scheme with the minimum maximum iron loss is selected, which is the design scheme of the rotor structure.

[0044] Finite element analysis is performed on the electric spindle motor with the optimized rotor structure, and its iron loss is calculated. The results are shown in Table 3. It can be seen from the table that, under the premise of meeting the average torque and torque fluctuation indicators, the iron loss is greatly reduced, which can effectively improve the heat dissipation of the electric spindle motor and improve the running stability and reliability.

[0045] Table 3 Comparison of finite element calculation results before and after rotor structure optimization

[0046]

Claims

1. A rotor structure of a high-speed electric spindle motor built into a CNC machine tool, characterized in that: The invention comprises a plurality of permanent magnet cavities arranged in pairs along the circumferential contour of the rotor. The motor is a built-in permanent magnet synchronous motor. The two permanent magnet cavities arranged in pairs are distributed in a "V" shape. The outer contour of the rotor is an uneven circumferential outer contour composed of arcs with different centers. A trapezoidal auxiliary groove is added at the position of the permanent magnet cavity edge at the upper side of the permanent magnet cavity close to the outer contour of the rotor.

2. The rotor structure according to claim 1, characterized in that: The specific outer contour of the uneven circle is: The initial structure of the rotor is a uniform circular outer contour, O is the center of the uniform circular outer contour, and the arc portion corresponding to the two "V"-shaped permanent magnet cavities arranged in pairs is taken. The "V"-shaped permanent magnet cavities are set to N pairs, and the degree of the arc portion corresponding to each pair of "V"-shaped permanent magnet cavities is , so that the radius of the rotor air gap and the position of the permanent magnet cavity remain unchanged, that is, |OR1|=|OO'|+|O'R1|, where R1 is the intersection of the midline of a pair of "V"-shaped distributed permanent magnet cavities and the outer contour of the rotor, O' is the changed center of the circle, and an arc is drawn with the changed O' as the center and O'R1 as the radius. R1 is the midpoint of the arc, P1 and P2 are the two end points of the arc, that is, the one-N outer contour P1P2 of the uneven circular outer contour of the rotor is obtained, P1 and P2 are the vertices at both ends of the arc respectively, and the one-N outer contour is arrayed along the circumference, that is, the uneven circular outer contour composed of arcs with different centers is obtained.

3. The rotor structure according to claim 2, characterized in that: The angle between the upper side and the lower side of the auxiliary groove and the permanent magnet cavity is in the range of 30° to 50°, and the width is in the range of 2 mm to 4 mm.

4. The rotor structure according to claim 3, characterized in that: The distance of the center O' of the uneven circumferential outer contour from the center O, the distance of the auxiliary slot from the rotor outer contour and the slotting distance of the auxiliary slot are set so that the iron loss of the electric spindle motor is minimized.

5. The rotor structure according to claim 4, characterized in that: The distance of the center O' of the uneven circumferential outer contour from the center O, the distance of the auxiliary slot from the rotor outer contour and the slotting distance of the auxiliary slot range from 5mm to 8mm, 2mm to 5mm and 3mm to 6mm respectively.

6. A method for designing a rotor structure according to any one of claims 1 to 5, characterized in that: include: Step (1) The electric spindle motor is a built-in permanent magnet synchronous motor, and the permanent magnet cavity adopts a "V" shape distribution; Step (2) determining that the initial structure of the rotor of the electric spindle motor is a uniform circular outer contour; Step (3) changing the outer contour of the rotor, changing the uniform circular outer contour into an uneven circular outer contour composed of circular arcs with different centers; Step (4) adding an auxiliary slot at the permanent magnet cavity; Step (5) optimizes the changed uneven rotor size to reduce the iron loss of the electric spindle motor.

7. The design method according to claim 6, characterized in that: Step (3) The method of changing the outer profile of the rotor is: The initial structure of the rotor is a uniform circular outer contour, O is the center of the uniform circular outer contour, and the arc portion corresponding to the two "V"-shaped permanent magnet cavities arranged in pairs is taken. The "V"-shaped permanent magnet cavities are set to N pairs, and the degree of the arc portion corresponding to each pair of "V"-shaped permanent magnet cavities is , so that the radius of the rotor air gap and the position of the permanent magnet cavity remain unchanged, that is, |OR1|=|OO'|+|O'R1|, where R1 is the intersection of the midline of a pair of "V"-shaped distributed permanent magnet cavities and the outer contour of the rotor, O' is the changed center of the circle, and an arc is drawn with the changed O' as the center and O'R1 as the radius. R1 is the midpoint of the arc, P1 and P2 are the two end points of the arc, that is, the one-N outer contour P1P2 of the uneven circular outer contour is obtained, P1 and P2 are the vertices at both ends of the arc respectively, and the one-N outer contour is arrayed along the circumference, that is, the uneven circular outer contour composed of arcs with different centers is obtained.

8. The design method according to claim 7, characterized in that: The method for adding the auxiliary slot in step (4) is as follows: a trapezoidal auxiliary slot is added at the position of the edge of the permanent magnet cavity, obliquely above the side of the permanent magnet cavity close to the outer contour of the rotor, wherein the angle between the upper and lower sides of the auxiliary slot and the permanent magnet cavity is in the range of 30° to 50°, and the width is in the range of 2 mm to 4 mm.

9. The design method according to claim 8, characterized in that: The steps for optimizing step (5) are as follows: Combined with the rotor structural parameters and processing requirements before motor optimization, the optimization variables and their value ranges are determined; the optimization variables are determined as follows: A-the distance from the center O' of the uneven circumferential outer contour to the center O; B-the distance from the auxiliary slot to the rotor outer contour; C-the slotting distance of the auxiliary slot; the value range of A is determined to be 5mm to 8mm, the value range of B is determined to be 2mm to 5mm, and the value range of C is determined to be 3mm to 6mm; Conducting experimental design and performing parametric scanning on multiple test schemes; the multiple test schemes include: the distance of the center O' of the uneven circumferential outer contour from the center O, the distance of the auxiliary slot from the rotor outer contour, and the slotting distance of the auxiliary slot are 5, 2, 3 or 6, 3, 4 or 7, 4, 5 or 8, 5, 6, in mm; The maximum iron loss, average torque and torque fluctuation obtained from each group of tests were calculated; Taking the average torque and torque fluctuation as constraints and minimizing the maximum iron loss as the optimization goal, the final values ​​of each optimization variable are obtained, that is, the rotor structure design scheme for reducing the iron loss of the electric spindle motor.

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