How to achieve precise braking of three-phase AC brake motor?

How to achieve precise braking of three-phase AC brake motor?
In industrial production, motors are an indispensable source of power, but have you ever thought about how motors achieve rapid braking when equipment needs to be stopped urgently? Especially in scenarios such as cranes, conveyors, and automated production lines, the "emergency braking" ability of motors directly affects the safety and production efficiency of the equipment. Today, we will unveil the braking principle of common three-phase AC brake motors in industry.

Why do we need a brake motor

After a power outage, the rotor of a regular three-phase asynchronous motor will continue to rotate for a period of time due to inertia before completely stopping. This' free parking 'method poses significant safety risks in industrial settings:

Crane: Heavy objects may slide down due to inertia, causing accidents.

Conveyor belt: Materials may pile up or fall off, affecting production efficiency.

Precision equipment: inaccurate positioning leading to product quality issues.

 

In order to solve these problems, brake motors have emerged. It can not only provide power, but also quickly brake after power failure, ensuring the safety and controllability of the equipment.

 

Braking principle of three-phase AC brake motor

 

The core function of the brake motor is rapid energy dissipation and precise locking. There are several common braking methods:

 

1. Electromagnetic braking: mechanical lock that stops immediately upon power failure

Electromagnetic braking is a common braking method in brake motors. The principle is:

When powered on: the electromagnet is engaged, the brake pads are separated from the motor shaft, and the motor runs normally.

When the power is cut off: the electromagnet loses power, the spring is pressurized, and the brake pads hold the motor shaft tightly, achieving rapid braking.

 

characteristic:

Short response time (usually less than 0.2 seconds).

The braking torque is large, up to twice the rated torque of the motor.

Suitable for situations that require emergency braking, such as cranes, elevators, etc.

 

Disadvantages:

Frequent starting and stopping can cause brake pad wear and require regular maintenance.

 

2. Reverse braking: Let the motor "defeat itself"

Reverse braking is achieved by changing the phase sequence of the motor power supply. The principle is:

After power failure, quickly switch the two-phase power line sequence to reverse the direction of the rotating magnetic field.

The rotor continues to rotate forward due to inertia, but is subjected to a reverse magnetic field, generating braking torque.

 

characteristic:

High braking torque, suitable for high-speed and heavy-duty situations.

It is necessary to cooperate with the speed relay to cut off the power when approaching zero speed, otherwise the motor will reverse.

 

Application scenarios:

Machine tool spindles, centrifuges, and other equipment that require rapid braking.

 

3. Energy consumption braking: converting kinetic energy into thermal energy

Energy consumption braking is achieved by injecting direct current into the stator winding of the motor. The principle is:

-After power failure, direct current is applied to the stator winding to generate a static magnetic field.

-The rotor cuts magnetic induction lines, generates eddy currents, and converts kinetic energy into thermal energy for consumption.

 

characteristic:

No mechanical wear, suitable for high-frequency braking situations.

An external braking resistor is required, which generates a large amount of heat.

Application scenarios:

CNC machining centers, automated assembly lines, and other equipment that require frequent braking.