Elevator

In an elevator system, the brake is a non-negotiable, life-critical safety component whose primary function is to hold the elevator car stationary at a floor. Elevators universally employ fail-safe, spring-applied, DC electromagnetic brakes that are integrated directly with the hoist motor and gearbox, known as the traction machine.

The operational principle is built around inherent safety:

1. Static Holding (Default State): Powerful mechanical springs exert a constant clamping force on a brake disc or drum coupled to the motor shaft. This is the brake’s default, unpowered state, ensuring the elevator car is securely held in place and cannot move.
2. Powered Release: When a user calls the elevator, the control system sends an electrical current to the brake’s electromagnetic coil at the same instant it sends power to the drive motor. The resulting magnetic field is strong enough to overcome the spring force, retracting the brake pads and releasing the brake just as the motor begins to turn.
3. Fail-Safe Engagement: The moment the car reaches the desired floor, the controller cuts power to both the motor and the brake coil. The magnetic field instantly collapses, and the springs re-apply the brake, smoothly and precisely stopping the car and holding it level with the floor. In any power outage scenario, this same action occurs, guaranteeing the elevator stops and remains safely in position.

Crucially, this primary electromagnetic brake is distinct from the elevator’s emergency “safeties”—the separate mechanical devices that are triggered by an overspeed governor to physically grip the guide rails in the rare event of a rope failure or uncontrolled descent. Modern safety standards (such as ASME A17.1/CSA B44) mandate extreme redundancy in the primary brake itself, often requiring dual electrical coils or mechanically independent brake calipers to ensure that no single point of failure can compromise the system’s holding capability.