EEJA Electro spindle knowledge

- Feb 23, 2020-

Electric spindle structure

The electric spindle is composed of motor without shell, spindle, bearing, spindle unit shell, drive module and cooling equipment. The motor rotor is made of pressing method and main shaft, which is supported by front and rear bearings. The stator of the motor is arranged in the shell of the spindle unit through a cooling sleeve device. The speed change of the spindle is controlled by the spindle drive module, while the temperature rise in the spindle unit is limited by the cooling equipment. The rear end of the spindle is equipped with a speed and angular displacement sensor, and the inner taper hole and the end face of the front end are used for the equipment tools.

Cooling of electric spindle

Because the electric spindle integrates the motor into the spindle unit, and the rotation speed is very high, a lot of heat will occur during the operation, which will cause the temperature rise of the electric spindle, and make the thermal and dynamic characteristics of the electric spindle worse, thus affecting the normal operation of the electric spindle. Therefore, it is necessary to adopt certain methods to control the temperature of the electric spindle to keep it constant within a certain value. Generally, the machine tool adopts the method of forced circulating oil cooling to cool the stator and main shaft bearing of the electric spindle. That is to say, the cooling oil passing through the oil cooling equipment circulates outside the stator and main shaft bearing of the main shaft compulsorily, taking away the heat generated by the high-speed rotation of the main shaft. In addition, in order to reduce the heat of the spindle bearing, the spindle bearing must be reasonably smooth.

Drive of electric spindle

The motor of the electric spindle adopts the AC asynchronous induction motor. Therefore, it is used in the high-speed machining machine tool. When starting, the speed should be increased from static state to tens of thousands or even hundreds of thousands of revolutions per minute. The starting torque is large, so the starting current should be 5-7 times higher than the rated current of the ordinary motor. There are two driving methods: frequency converter drive and vector control drive. The drive and control characteristic of the inverter is constant torque drive, and the output power is proportional to the torque. The latest inverter of machine tool adopts advanced transistor technology, which can complete the stepless speed change of spindle. The drive of vector control driver is constant torque drive at low speed and constant power drive at medium and high speed