Summary of the hottest ddmotor turntable design te

2022-07-27
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Overview of DD motor turntable design technology

dd motor (direct drive motor) is the product of the development of servo motor technology. The turntable driven by DD motor is another revolutionary application of direct drive technology in machining centers. Its structural feature is that the motor rotor is directly connected with the rotating workbench, and the motor stator is fixed with the mounting base to directly drive the turntable to realize the rotating movement. It eliminates the complex transmission parts such as gears, worm gears and so on, and has the following advantages: simple structure, large output torque, low noise, high speed and accuracy, easy control, convenient maintenance, high reliability

due to the special design of the motor structure, it can realize low-speed and high torque output, and meet the cutting and feeding needs of the turntable for the machine tool of the machining center; The motor has good servo rigidity and dynamic characteristics, which can increase the acceleration and rotation speed of the turntable. Since the stable operation of DD motor in the domestic coke market is directly connected with the rotating load, the "zero" transmission between the motor and the load is realized. Based on this, applying DD motor turntable to machining center will be a better choice

at present, many foreign manufacturers have produced and sold the following functions and features: selling such motors and turntables, such as Siemens and Cytec in Germany; In Japan, FANUC, Tsudakoma, etc., and in China, some units have purchased machine tools equipped with similar turntables, which are mainly used for gear processing

dd motor turntable common basic structure figure 1 shows the schematic diagram of common structural types of DD motor turntable, which is mainly composed of the following parts: (1) motor stator and rotor; (2) Bearings; (3) Encoder; (4) Turntable and rotating part; (5) Base, jacket and fixed part; (6) Sealing and dustproof structure required for DD motor turntable; (7) Circulating cooling structure

Figure 1 common structural types of DD motor turntable

configuration and selection of key components

1 Direct drive motor

at present, companies such as Siemens and Fanuc have direct drive motors that can be used for turntables. They have their own characteristics in terms of power, torque and speed, and their installation sizes are also different. They can be selected according to needs. In order to meet the use requirements of the turntable, the following three items shall be considered in the selection of motor:

1) maximum torque

the maximum torque shall meet the target requirements of load and rotating part acceleration. Namely: maximum torque ≥ inertia of moving part × Target acceleration + load torque

2) continuous torque

continuous torque is the torque that the turntable rotates continuously without overheating. Friction torque and cutting torque shall be considered when calculating the continuous torque. At the same time, if the turntable is tilted or used vertically and there is no braking or clamping structure, the torque effect caused by gravity needs to be considered. Since the performance of the motor is closely related to the thermal performance and cooling condition of the mechanical structure, sufficient margin must be reserved during selection

3) inertia

in order to give full play to the performance of the motor, the rotary inertia of the turntable should be as small as possible, and the inertia of the rotating part of the turntable (including the inertia of the load) should be strictly calculated to meet the requirements of the allowable rotary inertia of the motor

the inertia and rigidity of the turntable are a pair of contradictions, which can only be selected according to the user's requirements. In the actual selection, it is necessary to communicate with the motor manufacturer based on rigorous calculation to ensure the best selection

2. Bearing

dd motor turntable is usually supported by cross rolling. In the future, more factories will establish sub bearings, thrust/radial roller bearings or thrust angular contact ball bearings. Figure 2 shows the schematic diagrams of three kinds of bearings respectively. The actual design and selection can be comprehensively balanced according to the installation size, load, service life, etc

Figure 2 Schematic diagram of turntable support bearing

(a, B, C from left to right respectively)

figure 2A shows thrust/centripetal roller bearing. It can bear axial load, additional radial load and installation torque in both directions. It is especially suitable for bearing large overturning torque and has high rotation accuracy

figure 2B shows the cross roller bearing. The cylindrical rollers of the bearing are arranged perpendicular to each other on the 90 ° V-groove rolling surface through the spacing retainer. One bearing can bear the radial load, axial load, torque load and other loads in all directions

figure 2C shows thrust angular contact bearing. It can bear axial load, additional radial load and overturning moment in both directions, and is especially suitable for precision rotary table and high-speed rotary table. Its bearing capacity and rigidity are weaker than the above two bearings, but its high-speed performance is good

3. Encoder

dd motor turntable motor does not include encoder, so matching encoder must be selected in actual use to ensure motor position and speed feedback. The following three aspects should be paid attention to in the selection

first of all, pay attention to the target accuracy and the resolution of the rotary encoder. The best setting range is 10~20 times of the target accuracy. Second, pay attention to stability. Because the temperature of the encoder will rise with the temperature rise of the machine itself during use, resulting in a decline in accuracy, it is necessary to select an encoder with stable hot state function. Finally, attention should be paid to the matching with the motor and CNC system

turntable structure design the rubber tensile testing machine needs the following parameters in the process of testing

1 Sealed dust-proof structure

the rotor of the direct drive motor has permanent magnetism. If the metal dust in the processing area of the workbench enters the turntable, it will be adsorbed on the rotor, affecting the performance of the motor and even causing its failure. Therefore, it is usually necessary to adopt a combination of labyrinth structure and gas seal in the design to continuously blow clean and dry gas to ensure the safe and reliable operation of the motor

in terms of sealing, it must be fully considered that if the motor encounters coolant intrusion, its insulation will be reduced or degraded. In addition, the bearings and encoders used on the turntable are precision moving parts and detection elements, and the reliability of their sealing structure must be ensured in use

Figure 3 example of DD motor turntable

[from left to right are a Schaeffler company product, B DD turntable (structure diagram) developed by Beijing Machine Tool Research Institute, C ddm630 turntable developed by Beijing Machine Tool Research Institute for TH6363 product example]

2 Circulating cooling

the motor inside the turntable will generate heat during operation. If it is not handled properly, it will affect the accuracy and stability of the turntable and the machine tool. Therefore, slots shall be made on the stator sleeve of the turntable motor for circulating cooling, and circulating cooling water or oil shall be introduced to take away heat during operation. The acquisition of motor torque is related to the cooling of the motor. Only when the motor is effectively cooled can it reach its rated torque. However, excessive cooling will produce condensation, which will reduce the insulation of the motor. Therefore, the room temperature tracking cooling system is recommended

relatively speaking, the effect of water cooling is better than that of oil cooling. Under the condition of oil cooling, the maximum continuous torque of the motor will be lost by 20%. However, in the case of water cooling, rust prevention must be considered, so it is necessary to make choices according to different requirements and priorities

3. As the workbench of the machine tool, the brake

turntable needs the functions of indexing and accurate positioning. The direct drive motor installed on DD motor turntable is the same as the common servo motor. When receiving the stop command, its dynamic braking circuit will brake the motor

however, since there is no deceleration and transmission mechanism between DD motor turntable motor and turntable, the motor with very high speed will have a small angle of over rotation during emergency stop. Therefore, another mechanical or hydraulic locking mechanism is required in DD motor turntable to ensure accurate positioning. In the case of heavy cutting, it is also necessary to lock the turntable shaft. If the turntable is tilted or used vertically, the function of the brake mechanism will be more prominent

conclusion

in view of the good characteristics of DD motor turntable in terms of speed and torque, more manufacturers are committed to its development and practical application. With the growing maturity of DD motor motor, internationally mature turntable products have been well applied in machining centers

the technical features of DD motor turntable are briefly summarized above. However, there are still many specific problems to be further explored and solved by various turntable manufacturers in the actual design and assembly process. Compared with the international level, the domestic technical capacity in this field is still lagging behind, and it is extremely necessary to continuously promote the mature application of DD motor turntable in practical application, and achieve the effect of effectively improving the service performance of machine tools. (end)

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