Fault Phenomena and Troubleshooting Techniques for Electromagnetic Brakes

With the explosive development of the AGV industry, fail-safe electromagnetic brakes are widely used on AGVs to ensure safety. These brakes, also known as holding brakes, are the focus of this article, which discusses common faults, their causes, and installation and adjustment tips. The working principle of fail-safe electromagnetic brakes is that when the brake coil is powered, the armature releases the friction plates, allowing the motor shaft to rotate freely. In the event of an emergency stop or to prevent the AGV from rolling back, power is removed from the coil, causing the friction plates to be pressed and held by springs, locking the drive shaft in place.

As shown in the diagram, the electromagnetic brake consists of both electrical and mechanical components, so this article addresses faults and correct handling methods from both perspectives. A normal brake coil has a relatively low resistance. The resistance values of coils vary based on different power levels (or braking torque), typically ranging from several tens to hundreds of ohms. After disconnecting from the external circuit, a multimeter can be used to measure its resistance. If the resistance falls within this range, the coil is likely normal; an open or short circuit indicates a fault. Most brakes used in AGVs operate on low-voltage DC power, such as 24VDC, 48VDC, or 72VDC. The supply voltage and current must be adequate for normal operation, enabling the generation of sufficient electromagnetic force to fully release the armature.

If the brake coil is damaged or not provided with proper power, it will not release, causing the motor shaft to be locked. While assessing electrical faults is straightforward, mechanical issues are more complex but can still be traced to a few common types:

1. Loose friction plates: If the braking force does not meet the rated torque, the motor shaft may still rotate in the braking state.
   • 1.1 If the brake has been in use for a long time, normal wear may reduce the thickness of the friction plates too much. In this case, the working gap can be adjusted to increase friction force to achieve the rated torque. If wear exceeds acceptable limits, new friction plates should be replaced.
   • 1.2 If a new brake shows looseness, the gap may have been set too wide. Adjusting the reserved gap can restore proper clamping force to achieve rated torque.
2. Tight friction plates: If the friction plates are too tight, they may still exert resistance in the release state, causing excessive noise, overheating, or significantly higher driving current.
   • 2.1 Tight friction plates are typically caused by a small reserved air gap/magnetic gap, resulting in insufficient space for the armature to release the friction plates when engaged. Increasing the reserved gap can provide adequate rotation space.
   • 2.2 If the working surfaces of the brake are not parallel, misalignment may also lead to friction when the armature engages.
3. Inability to release friction plates: This occurs when the armature does not disengage even when the coil is powered, which is a more serious condition.
   • 3.1 This often happens due to a large magnetic gap that prevents sufficient electromagnetic force from overcoming the spring resistance, preventing armature engagement.
   • 3.2 Misalignment of the armature with the brake coil or foreign objects can prevent the armature from engaging.
   • 3.3 Coil damage or power supply issues can also lead to a lack of action from the armature.

While the symptoms of brake malfunctions can be complex, understanding the working principle allows for quick identification of issues. With proper adjustment and installation techniques, normal operation can be restored.