The current DC asynchronous motor is not designed for low inertia and high acceleration reaction. Do you really need servo motor?
Can an asynchronous motor with feedback device provide a better solution for special applications?
Looking at the definition and performance attributes of servo motor and asynchronous motor, you may get the answer. Servo motor system: servo system is not just a motor, it is a closed-loop motion system with controllers, drives, motors, and feedback devices, usually with optical or magnetic encoders.
Because suppliers are always advertising servo motors, people have conceptual confusion. 'Servo motor' is a permanent magnet (PM)
The synchronous machine represents a brushed or brushless permanent magnet motor.
Its performance properties are different from several other motor types.
The permanent magnet synchronous motor has high peak and continuous torque and can be used to drive the servo system with high acceleration and deceleration in the precise positioning system.
Torque is usually proportional to the input current, and the motor shaft speed is directly related to the input voltage.
The higher the input voltage, the faster the motor speed, and the torque/speed curve is linear. The permanent magnet structure is directly connected to the air gap of the motor.
Look at the configuration of permanent magnet brushless motor, movable rotor (Permanent Magnetic)
And the fixed stator coil interacts in magnetism to give the motor torque and speed.
The three-phase stator domain is alternately strengthened, and the permanent magnet rotor is synchronized with the rotating stator.
A special electronic communication system can be used to detect the position of the rotor to strengthen the stator coil.
In the precise positioning system, in addition to the use of super-large motors in most car applications and systems, permanent magnet brushless motors should be selected.
When used in closed-loop torque, speed or positioning system, permanent magnet brushless motor is only a servo motor.
Asynchronous Motors have the same physical stator as permanent magnet brushless motors, but the rotor structure is completely different.
The Squirrel Cage asynchronous motor includes a series of aluminum or copper parts embedded in the groove of the rotor structure and connected through a large short wing tail.
These rotor short plates are magnetic coupled with the stator rotation domain to generate a new rotor domain that interacts with the stator to make the rotor move.
There is a slight gap between synchronous stator, slow rotor domain and actual rotor speed, which leads to slip. The input frequency determines the motor speed.
For example, a 60Hz bipolar AC motor has a no-load speed of 3600 rpm, while a four-pole AC motor has a speed lower than 1800rpm and depends on a slip rate.
As the motor torque increases, the slip increases and the speed decreases.
To increase the torque of the AC asynchronous motor, the cost is to reduce the speed until the load reaches the critical point when the motor speed suddenly drops to zero.
An inherent AC motor performance feature is that its initial torque is small and there is no load when the motor starts.
This inherent torque-speed performance has been completely changed with the emergence of electric frequency converters in 1980s.
The function of the inverter is to re-determine the torque-speed curve with adjustable or variable drivers to change the voltage and frequency, thus making the AC asynchronous motor the King of system speed.
Today's speed and positioning system: continuous progress in high-performance driving has made AC asynchronous motors, permanent magnet brushless motors and corresponding drivers more competitive in the market, however, permanent magnet brushless motors still dominate the application of positioning control.
In addition, permanent magnet brushless motors are still eating in the factory. The DC brush speed is controlled at 1kw (1. 37hp)For a market with lower wattage applications.
How to choose: DC asynchronous motors are not currently designed for low hysteresis and high acceleration response.
It occupies the vast majority of the market share of speed applications from 100 watts to 1 million watts. Except at 50kw (67hp)
For larger systems, permanent magnet brushless motors can be used for servo positioning systems.
AC asynchronous motors are more used in fixed or variable speed systems. Common solutions make it rare.
Other motors are also good, but far less successful than classic AC asynchronous motors and emerging permanent magnet brushless motors.