AC motor is a machine used to realize the mutual conversion of mechanical energy and AC electrical energy. As the AC power system is a huge development, AC motor has become the most commonly used motors. AC motors and DC motors compared, since there is no commutator (see commutated DC motor), the structure is simple, easy to manufacture, is strong, easy to make high-speed motors, high voltage, high current, high capacity. The power coverage of AC motors is very large, from a few watts to hundreds of thousands of kilowatts, or even millions of kilowatts. In the early 1980’s, the largest steam turbine generator has reached 1.5 million kilowatts.
According to statistics, AC motors can be classified in the following two ways:
AC motors usually divided according to their functions alternators , AC motors and synchronous condenser categories. Since the reversibility of the motor operating state, both the same motor as a generator but also as a motor .
The division of motors into generators and motors is not very precise, but some motors are mainly used as generators, and some motors are mainly used as motors.
AC motor by species divided synchronous motors , asynchronous motors into two categories. Ns synchronous rotor speed of the rotating magnetic field at the same speed, called the synchronous speed. ns and the connected alternating current frequency (f), the poles of the machine have a strict relationship between the number (P) pair.
In China, the power frequency is 50 Hz, the three-phase AC motor in a pair of pole motor the synchronous speed of 3000 rev / min, two pairs of three-phase AC motor pole motor synchronous speed of 1500 rev / min, I analogy. The speed of the rotor of an asynchronous motor is always lower or higher than the speed of its rotating magnetic field, hence the name of asynchronous. The difference between the rotor speed of the asynchronous motor and the rotating magnetic field speed (called slip) is usually within 10%.
AC motor is a very broad classification. The type of motor itself is very large. AC motor itself can also be divided into low speed and high speed. Low speed can be called low speed motor, AC low speed motor, and high speed can be called high speed motor, high speed motor, and AC high speed. Motor, and high-speed motor can be called electric spindle, high-speed electric spindle and so on.
Electric spindle in recent years in CNC machine tools will appear in the field of machine tool spindles and spindle motor integration of new technologies, it linear motor technology, high-speed cutting tool technology together, will put into a new era of high-speed machining. The electric spindle is a set of components, which includes the electric spindle itself and its accessories: electric spindle, high frequency frequency conversion device, oil mist lubricator, cooling device, built-in encoder, and tool change device.
The technology integrated by the electric spindle:
High speed bearing technology: electric spindle usually composite ceramic bearings , wear resistant, the conventional bearing life is several times; sometimes with electric levitation bearing or hydrostatic bearing , does not contact the inner and outer rings, theoretically unlimited life;
High-speed motor technology: The electric spindle is the product of the fusion of the motor and the spindle. The rotor of the motor is the rotating part of the spindle. Theoretically, the electric spindle can be regarded as a high-speed motor. The key technology is dynamic balance at high speed;
Lubrication: The lubrication of the electro-spindle generally adopts regular and quantitative oil and gas lubrication; grease lubrication can also be used, but the corresponding speed should be discounted. The so-called timing is to inject oil at regular intervals. The so-called quantitative means to precisely control the amount of lubricating oil each time through a device called a quantitative valve. The oil-air lubrication refers to that the lubricating oil is blown into the ceramic bearing with the compressed air. Oil control is very important. Too little will not provide lubrication; too much will cause heat due to oil resistance when the bearing rotates at high speed. Cooling device: In order to dissipate heat for the high-speed electric spindle as soon as possible, a circulating coolant is usually passed to the outer wall of the electric spindle. The function of the cooling device is to maintain the temperature of the coolant.
Built-in pulse coder : To achieve the automatic tool change and a rigid tapping, spindle built a pulse encoder to achieve accurate phase angle control and the feed fit.
Automatic tool changer : For use in machining centers , equipped with an automatic tool change spindle apparatus comprises a disc spring, broach cylinder and the like;
How to install high-speed tools: The widely-familiar BT and ISO tools have been proved to be unsuitable for high-speed machining. In this case, high-speed tools such as HSK and SKI appeared.
High frequency frequency conversion device: In order to realize the speed of tens of thousands or even hundreds of thousands of revolutions per minute of the electric spindle, a high frequency frequency conversion device must be used to drive the built-in high-speed motor of the electric spindle, and the output frequency of the frequency converter must reach thousands or several kilohertz. .
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