Manufacturing method a motor to reduce cogging torque
By measuring and assembling rotor and stator orders using Fourier transforms to control cogging torque, the method reduces motor defects and associated costs, enhancing manufacturing efficiency and quality.
Patent Information
- Authority / Receiving Office
- KR · KR
- Patent Type
- Patents
- Current Assignee / Owner
- 주식회사 메텍
- Filing Date
- 2024-05-28
- Publication Date
- 2026-07-29
AI Technical Summary
Conventional motor manufacturing methods result in a high discard rate due to excessive cogging torque, leading to increased management costs and inefficiencies, as they rely on post-assembly inspection and discarding motors exceeding a standard value.
A method involving measuring and decomposing the orders of individual rotor and stator components using Fourier transforms, then assembling them to ensure the combined amplitude of their orders does not exceed a predetermined reference value, thereby reducing cogging torque.
Minimizes motor defects by ensuring cogging torque remains below a reference value, reducing noise and vibration, and minimizing waste and management costs.
Smart Images
Figure 112024057954123-PAT00001_ABST
Abstract
Description
Technology Field
[0001] The present invention relates to a method for manufacturing a motor that reduces cogging torque, and more specifically, to a method for manufacturing a motor that can reduce cogging torque by combining the respective orders of the rotor and the stator. Background Technology
[0002] The primary sources of electromagnetic noise and vibration in permanent magnet drive motors are torque ripple and cogging torque caused by electric forces. Cogging torque is a torque generated by the magnetic resistance between the rotor's permanent magnets and the stator's electromagnets; its magnitude varies with rotational position, while its period is determined by the number of rotor permanent magnets and stator electromagnets based on rotational speed. Torque ripple, on the other hand, represents non-linear torque fluctuations that encompass various factors during motor rotation under load. The causes of such torque ripple include cogging, the interaction between Magneto-Motive Force (MMF) and high-frequency air gap flux, and the geometry of the rotor and stator.
[0003] The cogging torque of a permanent magnet motor is caused by the distribution of the magnetic field produced by the permanent magnet, and its strength varies due to the non-uniform magnetization of the magnet, and is caused by machining errors of the magnetization yoke, non-uniformity of the position of the magnetization winding within the slot, and positional errors of the magnet within the magnetization yoke.
[0004] While the application of high-performance permanent magnets in recently developed electric motors has enabled high output in small motors, vibration and noise increase due to the cause of cogging torque. Prior art literature
[0005] Registered Patent No. 10-2151421 (Registration Date: August 28, 2020) Registered Patent No. 10-0118681 (Registration Date: July 22, 1997) Published Patent No. 10-2006-0115506 (Publication Date: November 9, 2006) Published Patent No. 10-2009-0075745 (Publication Date: July 8, 2009) The problem to be solved
[0006] Conventional motor manufacturing methods involved assembling the rotor and stator, then assembling the rotor and stator in any combination, and finally inspecting the motor's cogging torque. If the cogging torque of the assembled motor was below a standard value, it was shipped; if it exceeded the standard, it was discarded. This method presented problems, such as a large number of defective products being discarded and increased management costs due to the strict limitations on recycling when discarded.
[0007] The present invention aims to solve the above-mentioned problems. The present invention aims to provide a method for manufacturing a motor capable of reducing cogging torque, which is a cause of vibration and noise. means of solving the problem
[0008] The motor manufacturing method according to the present invention is characterized by measuring the order of a rotor and measuring the order of a stator, and assembling a motor by combining the rotor and the stator such that the amplitude of the sum of the order of the rotor and the order of the stator does not exceed a predetermined reference value at a constant rotational speed.
[0009] In addition, the above motor manufacturing method preferably includes a rotor measurement step, a stator measurement step, a combination step, and an assembly step. The rotor measurement step involves mounting the rotor on a dummy stator to measure and store the order of the rotor. The stator measurement step involves mounting the stator on a dummy rotor to measure and store the order of the stator. The combination step involves combining the rotor and the stator such that the amplitude of the sum of the order of the rotor and the order of the stator does not exceed the reference value at the constant rotational speed, based on the stored order of the rotor and the stored order of the stator. The assembly step involves assembling the combined rotor and the stator.
[0010] In addition, in the above-described motor manufacturing method, the rotor measurement step comprises a first rotation step, a first torque measurement step, a first disassembly step, and a first storage step. The first rotation step involves mounting the rotor on the dummy stator and rotating it at a constant rotational speed. The first torque measurement step measures the cogging torque during the first rotation step. The first disassembly step performs a Fourier transform on the cogging torque measured during the first torque measurement step to decompose it into the order of the dummy stator and the rotor. The first storage step stores the order of the rotor decomposed during the first disassembly step.
[0011] In addition, in the motor manufacturing method described above, the stator measurement step comprises a second rotation step, a second torque measurement step, a second disassembly step, and a second storage step. The second rotation step involves mounting the stator onto the dummy rotor and rotating it at a constant rotational speed. The second torque measurement step measures the cogging torque during the second rotation step. The second disassembly step performs a Fourier transform on the cogging torque measured during the second torque measurement step to decompose it into the order of the dummy rotor and the stator. The second storage step stores the order of the stator decomposed during the second disassembly step. Effects of the invention
[0012] According to the present invention, the cogging torque of a motor can be reduced by selecting and assembling the rotor and stator such that the amplitude of the sum of the rotor order and the stator order does not exceed a certain reference value. Therefore, motor defects caused by cogging torque can be minimized during the manufacturing stage. Brief explanation of the drawing
[0013] FIG. 1 is a conceptual diagram of one embodiment of a motor manufacturing method according to the present invention, FIG. 2 is a conceptual diagram of the rotor measurement step in the embodiment of FIG. 1, FIG. 3 is a conceptual diagram of the stator measurement step in the embodiment of FIG. 1, Figure 4 is a conceptual diagram of the Fourier transform. Specific details for implementing the invention
[0014] With the development of permanent magnet synchronous motors, cogging torque generated by the interaction between stator teeth and rotor permanent magnets reduces motor control precision and causes noise and vibration; consequently, extensive research is being conducted to reduce this cogging torque. However, most existing studies on cogging torque reduction focus on reducing the average value of the fundamental order component of the cogging torque, which corresponds to the least common multiple of the number of poles and slots of the motor.
[0015] When motors are mass-produced, cogging torque occurs in the majority of cases not only with a component corresponding to the least common multiple of the number of poles and slots, but also with a component corresponding to a multiple of both the number of poles and slots. For example, when mass-producing 10-pole, 12-slot motors, most motors exhibit cogging torque of the 60th order (the least common multiple of the number of poles and slots), as well as 10th and 12th order components. This phenomenon occurs when the magnetic distribution of the rotor or stator shape is asymmetric. Such magnetic asymmetry arises during the motor manufacturing process. For example, asymmetry in the dimensions, position, and magnetization levels of permanent magnets, asymmetry in the stator or rotor shape, and eccentricity cause magnetic asymmetry.
[0016] Various methods exist to reduce cogging torque, including increasing the air gap length, using fractional slots, stator notches, and stator or rotor skew. Among these, skew is the most useful method. However, if the magnetic distribution of the rotor or stator geometry is asymmetric, cogging torque cannot be eliminated by the skew geometry. In a 10-pole 12-slot motor with a rotor and stator having asymmetric magnetic distribution, only the 60th-order component of cogging torque is eliminated by the skew geometry, while the 10th and 12th-order components remain unchanged; therefore, a robust design method is required to reduce cogging torque caused by manufacturing tolerances during the motor production process.
[0017] Meanwhile, the Fourier transform expresses an arbitrary input signal by decomposing it into a sum of periodic functions with various frequencies. That is, the periodic functions used in the Fourier transform are sin and cos trigonometric functions, and the Fourier transform decomposes the original signal into sin and cos functions across various frequency bands, ranging from high to low frequencies. For example, as shown in Figure 4, when the time-series input signal, such as the red signal at the beginning, is Fourier transformed, the individual periodic function components are obtained. Each periodic function component has its own frequency and amplitude, and when all of them are combined, they become the original red signal.
[0018] A motor is completed by assembling a rotor and a stator. In other words, the motor is disassembled into a rotor and a stator; therefore, the motor's cogging torque is the sum of the individual cogging torques of the rotor and the stator. Thus, the present invention measures the respective order of the rotor and the stator and assembles them so that the amplitude values of these orders do not exceed a reference value at a constant speed.
[0019] Accordingly, one embodiment of the motor manufacturing method according to the present invention will be explained with reference to FIGS. 1 to 3.
[0020] The motor manufacturing method according to the present invention measures the respective order of a plurality of rotors and a plurality of stators. Then, a motor is assembled by combining rotors and stators such that the amplitude of the sum of the order of the rotors and the order of the stators does not exceed a predetermined reference value at a constant rotational speed.
[0021] More specifically, the motor manufacturing method according to the present invention includes a rotor measurement step (S10), a stator measurement step (S20), a combination step (S30), and an assembly step (S40).
[0022] The rotor measurement step (S10) measures and stores the order of the rotor by mounting the rotor on a dummy stator. Since the order of the rotor is not identical and varies from product to product due to manufacturing tolerances during the manufacturing process, the rotor measurement step (S10) measures and stores the order of each rotor.
[0023] To explain this in more detail, the rotor measurement step (S10) includes a first rotation step (S11), a first torque measurement step (S13), a first disassembly step (S15), and a first storage step (S17).
[0024] The first rotational stage involves mounting a rotor onto a dummy stator and rotating it at a constant rotational speed. The dummy stator is designed so that the rotor can be easily mounted and detached to measure the order of the rotor. Thus, multiple rotors are mounted on the dummy stator to facilitate the measurement of the order of each rotor.
[0025] The first torque measurement step (S13) measures the cogging torque in the first rotation step (S11). That is, it measures the cogging torque of an assembly in which a rotor is mounted on a dummy stator.
[0026] The first decomposition step (S15) performs a Fourier transform on the cogging torque measured in the first torque measurement step (S13) to decompose it into the orders of the dummy stator and rotor. That is, since the cogging torque measured in the first torque measurement step (13) pertains to an assembly of the dummy stator and rotor, the orders of the dummy stator and rotor are summed. Therefore, when a Fourier transform is performed, the orders of the dummy stator and rotor are decomposed.
[0027] The first storage step (SS17) stores the order of the rotor disassembled in the first disassembly step (S15). The order of each rotor produced through the rotor measurement step (S10) is stored.
[0028] The stator measurement step (S20) measures and stores the order of the stator by mounting the stator on a dummy rotor. The dummy rotor is designed so that the stator can be easily mounted and separated to measure the order of the stator, just like the dummy stator. Thus, multiple stators are mounted on the dummy rotor to facilitate the measurement of the order of each stator. To this end, the stator measurement step (20) includes a second rotation step (S21), a second torque measurement step (S23), a second disassembly step (S25), and a second storage step (S27).
[0029] The second rotation step (S21) involves mounting a stator on a dummy rotor and rotating it at a constant rotational speed.
[0030] The second torque measurement step (S23) measures the cogging torque in the second rotation step (S21).
[0031] The second decomposition step (S25) performs a Fourier transform on the cogging torque measured in the second torque measurement step (S23) to decompose it into the order of the dummy rotor and stator.
[0032] The second storage step (S27) stores the order of the stator disassembled in the second disassembly step (S25).
[0033] The degree of each stator produced through the stator measurement step (S20) is stored.
[0034] The combination step (S30) combines the rotor order stored in the rotor measurement step (S10) and the stator order stored in the stator measurement step (S20) so that the amplitude of the sum of the rotor and stator orders does not exceed a reference value at a constant rotational speed. That is, the rotor and stator are combined so that the amplitude of the sum of the frequencies does not exceed the reference value.
[0035] The assembly step (S40) assembles the rotor and stator combined in the combination step (S30).
[0036] In this embodiment, the order of the rotor and the order of the stator are measured first, and then the rotor and stator are assembled by combining them such that the amplitude of the sum of the orders of the rotor and stator does not exceed a reference value at a constant speed. By assembling the rotor and stator in this way, the cogging torque of the motor does not exceed the reference value.
Claims
Claim 1 A method for manufacturing a motor characterized by comprising: a rotor measurement step of mounting a rotor on a dummy stator and rotating it, and then measuring and storing the order of the rotor; a stator measurement step of mounting a stator on a dummy rotor and rotating it, and then measuring and storing the order of the stator; a combination step of combining the rotor and the stator such that the amplitude of the sum of the order of the rotor and the order of the stator does not exceed a predetermined reference value at a constant rotational speed, with respect to the stored order of the rotor and the stored order of the stator; and an assembly step of assembling the combined rotor and the stator. Claim 2 A method for manufacturing a motor according to claim 1, wherein the rotor measurement step comprises a first rotation step of mounting the rotor on the dummy stator and rotating it at a constant rotational speed, a first torque measurement step of measuring the cogging torque in the first rotation step, a first decomposition step of performing a Fourier transform on the cogging torque measured in the first torque measurement step to decompose it into the order of the dummy stator and the rotor, and a first storage step of storing the order of the rotor decomposed in the first decomposition step. Claim 3 A method for manufacturing a motor according to claim 1, wherein the stator measurement step comprises a second rotation step of mounting the stator on the dummy rotor and rotating it at a constant rotational speed, a second torque measurement step of measuring the cogging torque in the second rotation step, a second decomposition step of decomposing the cogging torque measured in the second torque measurement step into the order of the dummy rotor and the stator by performing a Fourier transform, and a second storage step of storing the order of the stator decomposed in the second decomposition step. Claim 4 delete