What is an asynchronous motor? What is a torque motor? What is the difference between the two?

Electric motors are commonly called motors, and they are found in many devices. This article will introduce asynchronous motors, torque motors, and the differences between torque motors and asynchronous motors.

1. Asynchronous motor

An asynchronous motor, also known as an induction motor, is an AC motor that converts electromechanical energy into mechanical energy by generating electromagnetic torque through the interaction between the rotating magnetic field of the air gap and the induced current of the rotor winding.

Three-phase asynchronous motors are mainly used as motors to drive various production machinery, such as fans, pumps, compressors, machine tools, light industry and mining machinery, threshers and crushers in agricultural production, processing machinery for agricultural and sideline products, etc. They have simple structure, easy manufacturing, low price, reliable operation, durability, high operating efficiency and applicable working characteristics.

The asynchronous motor was invented by Italian physicist and electrical engineer Ferraris in 1885. In 1888, he presented an experimental report that gave a rigorous scientific description of the rotating magnetic field, laying the foundation for the subsequent development of asynchronous motors and self-starting motors. Ferraris believed that the scientific value of his theory of rotating magnetic fields and the new products he developed far exceeded their material value, so he deliberately did not apply for a patent for his invention, but demonstrated these latest achievements to the public in the laboratory. He also advocated the use of alternating current systems. In the same year, Nikola Tesla obtained a patent for the induction motor in the United States. A year later, Mikhail Dolivo-Dobrovolsky invented the cage asynchronous motor. The development of asynchronous motors is rapid. For asynchronous motors of the same size, the rated power has developed from 5.5kW in 1897 to 74.6kW in 1976. The squirrel cage asynchronous motor is the most widely used asynchronous motor.

2. Torque Motor

A torque motor is a motor that directly outputs torque. Its torque is proportional to the current, so the torque and speed can be controlled by controlling the current. Torque motors are generally suitable for occasions that require precise control of torque and speed, such as industrial robots, CNC machine tools, textile machinery, etc.

Principle of torque motor: Torque motor can ensure constant torque in a wide speed range. It is suitable for transmission occasions that require constant torque when changing speed in two gears. For example, in printing and dyeing machinery, when the fabric is transmitted through several rollers, the fabric is not wrapped around the rollers, but attached to the surface of the rollers for driving. The diameter of the rollers does not change. In this case, torque motors should be used to ensure constant torque and constant tension of the fabric at any speed.

Torque motors are allowed to run at low speed for a long time (even stop running), and they heat up severely. External blowers are usually used to force air cooling. When using torque motors, check whether the blower is running well. There should be good ventilation around the blower, and dry and flammable items are not allowed. There is no flammable dust or volatile oil nearby.

Taking into account the different application conditions, the mechanical winding or transmission driven by the torque motor has different materials and specifications, requiring different tensions. The torque of the torque motor or variable speed motor is required to be adjusted within a certain range, and the voltage applied to the torque motor is usually adjusted to meet these requirements. When the input voltage of the torque motor changes, a voltage regulator is usually used. In order to improve the strength and adjustment accuracy of the mechanical characteristics, the thyristor negative feedback control circuit can also be used for stepless speed regulation, but the system is more complicated.

3. The difference between torque motor and asynchronous motor

There are several important differences between torque motors and asynchronous motors:

Different working principles: Torque motors work based on hysteresis, while asynchronous motors work based on electromagnetic induction. There is magnetic damping between the rotor and stator of a torque motor, so when the load increases, it can maintain a relatively stable speed and output torque, while asynchronous motors may experience speed and torque fluctuations when the load changes.

Different speed ranges: Torque motors generally have higher starting torque and a wider speed range, while asynchronous motors are generally suitable for low to medium power and lower speed applications.

Different efficiency and accuracy: Torque motors generally have higher efficiency and accuracy because they can control rotor position and speed. The efficiency and accuracy of asynchronous motors may be affected by rotor slip.

Different control methods: Due to their different working principles and characteristics, torque motors and asynchronous motors require different control methods. Torque motors usually require more complex controllers and algorithms to achieve precise position and speed control, while asynchronous motors can achieve speed regulation through simple inverter control.