introduction

DD motor (direct drive motor), as a high-precision driving device, has been widely used in industrial automation, semiconductor manufacturing, laser processing and other fields. However, the cogging effect is one of the key factors affecting the performance of DD motors, which can cause torque fluctuations, vibrations, and noise, reducing the positioning accuracy and stability of the system. Therefore, studying the low cogging effect design method of DD motors has important theoretical and practical significance.

The mechanism of tooth groove effect

The cogging effect is caused by the interaction between the stator cogging of the motor and the rotor permanent magnet. When the rotor rotates, the relative position between the permanent magnet and the stator slot constantly changes, causing periodic changes in the air gap magnetic flux, which in turn causes fluctuations in the magnetic reluctance torque. This torque fluctuation will be transmitted to the mechanical system, generating vibration and noise, affecting the operational accuracy and reliability of the equipment.

Design method for low tooth slot effect

1. Magnetic pole optimization design

The shape and size of magnetic poles have a significant impact on the cogging effect. By optimizing the magnetic pole design, the distribution of air gap magnetic field can be changed to reduce cogging torque. For example, by adopting a skewed pole design, the magnetic poles are tilted at a certain angle in the circumferential direction, so that the magnetic fields of adjacent poles are spatially offset, thereby reducing the peak torque of the tooth groove. In addition, magnetic pole segmentation design can be adopted, dividing the magnetic pole into several small segments with a certain interval between each segment. By adjusting the magnetic field strength and phase of each segment of the magnetic pole, the cogging torque can be further reduced.

2. Optimization design of stator slot

The shape and size of the stator slots are also important factors affecting the slot effect. By optimizing the stator slot design, the uniformity of the air gap magnetic field can be improved and the slot torque can be reduced. A common method is to use stator tooth shoe design, which adds a shoe at the end of the stator teeth to expand the air gap area and reduce the rate of change in air gap magnetic conductivity. In addition, a stator tooth groove design can be adopted, which means that the stator teeth are inclined at a certain angle in the circumferential direction, so that the magnetic fields of adjacent tooth grooves are spatially offset, thereby reducing the tooth groove torque.

3. Optimization design of permanent magnets

The shape, size, and arrangement of permanent magnets also have a certain impact on the cogging effect. By optimizing the design of permanent magnets, the waveform of the air gap magnetic field can be improved and the cogging torque can be reduced. For example, using Halbach array permanent magnet structure, by arranging the polarity of the permanent magnets reasonably, the air gap magnetic field is approximately sinusoidal distributed in the circumferential direction, thereby reducing the cogging torque. In addition, a segmented design of permanent magnets can be adopted, dividing the permanent magnets into several small sections with a certain interval between each section. By adjusting the magnetic field strength and phase of each section of the permanent magnet, the cogging torque can be further reduced.

4. Winding optimization design

The distribution and connection method of windings also have a certain impact on the cogging effect. By optimizing the winding design, the inductance characteristics of the motor can be changed to reduce cogging torque. For example, adopting a fractional slot winding design, which does not use an integer ratio between the number of stator slots and the number of rotor poles, reduces the harmonic content of the air gap magnetic field, thereby reducing the cogging torque. In addition, a distributed winding design can be adopted to distribute the windings in multiple stator slots. By adjusting the number of turns and connection method of the windings reasonably, the cogging torque can be further reduced.

5. Structural optimization design

In addition to the optimization design of the magnetic poles, stator slots, permanent magnets, and windings mentioned above, the cogging effect can also be reduced through structural optimization design. For example, adopting a coreless structure to eliminate the cogging effect of the stator core; Alternatively, an air gap structure can be adopted to increase the length of the air gap and reduce the rate of change in air gap magnetic conductivity. In addition, a flexible connection structure can be used to isolate the transmission of cogging torque between the motor and the load, reducing system vibration and noise.

Application case of low tooth slot effect design method

1. Applications in semiconductor manufacturing equipment

In semiconductor manufacturing equipment, such as wafer handling robots, lithography machines, etc., there are extremely high requirements for positioning accuracy and stability. The DD motor designed with low cogging effect can effectively reduce cogging torque, improve the positioning accuracy and stability of the equipment. For example, a certain wafer handling robot adopts a DD motor with slanted pole design and stator tooth shoe design, which reduces the cogging torque by more than 50% and achieves a positioning accuracy of ± 1 μ m, meeting the high-precision requirements of semiconductor manufacturing.

2. Application in laser processing equipment

In laser processing equipment, such as laser cutting machines, laser welding machines, etc., high-speed and high-precision motion control is required. The DD motor designed with low cogging effect can improve the smoothness of equipment movement and machining accuracy. For example, a certain laser cutting machine adopts a Halbach array permanent magnet structure and a DD motor with fractional slot winding design, which reduces cogging torque by more than 30%, increases cutting speed by 20%, and significantly improves cutting quality.

3. Applications in industrial robots

In industrial robots, such as articulated robots and parallel robots, it is necessary to achieve multi axis coordinated motion. The DD motor designed with low cogging effect can improve the motion accuracy and repetitive positioning accuracy of robots. For example, a certain articulated robot adopts a DD motor with a large air gap structure and flexible connection structure, which reduces the cogging torque by more than 40% and achieves a repeat positioning accuracy of ± 0.01mm, meeting the high-precision motion requirements of industrial robots.

conclusion

The cogging effect is one of the key factors affecting the performance of DD motors. Through various methods such as magnetic pole optimization design, stator cogging optimization design, permanent magnet optimization design, winding optimization design, and structural optimization design, the cogging effect can be effectively reduced and the performance of DD motors can be improved. In practical applications, it is necessary to select appropriate design methods based on specific application requirements and working environments, and optimize combinations to achieve the best low cogging effect effect. With the continuous development of motor technology and control technology, the low cogging effect design method will be continuously improved and innovated, providing more reliable technical support for the application of DD motors in various fields.