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The Structure And Working Principle Of AC Torque Motor

The operating principle of the AC torque motor is exactly the same as that of the general squirrel-cage asynchronous motor, but the structure is different. It uses materials with high resistivity (such as brass, constantan, etc.) as the guide bars and terminal ring of the rotor. Therefore, the rotor resistance of a torque motor is much greater than that of a normal squirrel-cage motor.
The mechanical characteristics of torque motors are different from ordinary squirrel cage motors. Due to different design parameters, the mechanical characteristics and uses of torque motors are divided into two categories: torque motors with winding characteristics and torque motors with constant torque characteristics.

The Structure And Working Principle Of AC Torque Motor插图

Winding characteristic torque motor, realizing constant tension transmission, suitable for occasions that need to maintain constant tension of the product and wind the product on the roller at a constant line speed during the production process, for example, on printing and dyeing machinery, winding fabrics Roller, as the fabric is wound onto the roller, the diameter of the roller gradually increases and the load increases accordingly.

It can be seen from the mechanical characteristics of the torque motor that when the load increases, the speed automatically decreases, thereby maintaining a certain line speed and tension, and achieving the process requirements. This kind of torque motor is often used in textiles, printing, dyeing, paper making, rubber, wire, cable, etc.

The constant torque characteristic torque motor can make the torque basically constant in a generally wide speed range and is suitable for transmission occasions that require constant torque when the two speeds change.

For example, in printing and dyeing machinery, when several rollers are used to convey the fabric, since the fabric is not wound on the rollers, but only attached to the surface of the rollers and driven by them, the diameter of the rollers does not change.

The motor with constant torque characteristic is used to ensure that the torque is constant and the tension of the fabric is constant at any speed.

The Structure And Working Principle Of AC Torque Motor插图1

The torque motor allows long-term low-speed operation (even blocked), and its heat is very serious, and an external blower is usually used to force air cooling.

When using a torque motor, pay attention to check whether the blower is in good condition, there should be a good ventilation environment around it, and no dry combustibles, combustible dust, or volatile combustible oils are allowed to approach.

Due to the different use conditions, the types and specifications of the materials wound or transmitted by the machinery driven by the torque motor are different, and the required tension is different. It is required to adjust the torque of the torque motor, or to change the speed within a certain range, usually by adjusting the voltage applied to the torque motor to achieve these requirements.

To change the input voltage of the torque motor, a voltage regulator is usually used. In the case where the hardness of the mechanical characteristics and the adjustment accuracy are required to be improved, the thyristor speed negative feedback control circuit can also be used for stepless speed regulation, but the system is more complicated.

The common forms of regulator adjustment are as follows:

(1) Three-phase balance adjustment. The three-phase regulator is used, connected in a star connection, coaxial control, and the three-phase voltage is adjusted at the same time to make it balanced. The torque motor can run in a balanced state, with a wide adjustment range and good effect, but a three-phase voltage regulator is required. , not very economical.

(2) Two-phase voltage regulation. Use two single-phase voltage regulators for a U-shaped connection and coaxial adjustment. For example, when adjusting the two phases of A and C, the sliding brushes a and c of the voltage regulator slide symmetrically at the same time, which can also achieve balanced adjustment.

However, when using this method, it must be noted that the terminal voltage of the U-shaped single-phase voltage regulator is the power line voltage, and the rated voltage of the single-phase voltage regulator used should be adapted to the requirements of the power line voltage.

Most of the single-phase voltage regulators currently produced have a rated voltage of 220V, so they cannot be used in ordinary three-phase 380V power supply systems, but can only be used in systems with three-phase 220V power supply voltage.

(3) Single-phase regulation. Single-phase regulation uses only one single-phase voltage regulator to regulate the voltage of one phase. The torque motor operates in an unbalanced state, and the adjustment performance is poor.

However, due to the simple equipment, this adjustment form is widely used. The commonly used single-phase voltage regulation methods are as follows: A. The voltage regulator is connected between the two phases. B. The voltage regulator is connected between one phase and the zero line. When using single-phase regulation, it should be noted that after the voltage regulator is adjusted to a voltage lower than a certain value, negative torque will appear at a certain speed.

When the voltage is adjusted to 0V, negative torque will appear in the whole speed range. If the torque motor drives things such as textiles or plastics, paper, etc., the tension will be abnormal because there is a braking torque in the motor at this time. The reason for the negative torque is due to the soft nature of the torque motor.

The Structure And Working Principle Of AC Torque Motor插图2

Because the torque motor is a special motor, please do not use the working principle of the ordinary asynchronous motor to analyze it. For example, the torque motor can run in a locked rotor for a long time.

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