Holding Brake

A brake mounted on a motor or joint that automatically locks the shaft when power is cut.

A holding brake is usually electromagnetic: when powered, an electromagnet pulls the friction plates apart so the motor can turn freely; when power is cut, a spring clamps the friction plates together and the shaft is locked, which is why it's sometimes called “fail-safe” or power-off braking. Its job is to hold a joint in place during a power loss, an emergency stop, or when the drive is disabled, so an arm doesn't fall under gravity and hurt someone or damage something; it's mainly for holding position, not for braking during high-speed motion. Most industrial and collaborative robot-arm joint modules include one. The trade-off is added weight, size, and cost, so some quadruped and humanoid robot joints skip the brake entirely and go limp when power is cut, which is why testing often uses a safety gantry. Whether a joint module has a brake, and how much torque that brake can hold, are common specs to check.

ExampleWhen an emergency stop is pressed on a collaborative arm and it stays frozen in mid-air instead of dropping, that's the holding brakes in each joint at work.

Also called

Brake, Electromagnetic Brake

Related

Joint Actuator Module · Emergency Stop · Safe Torque Off (STO) · Servo Enable (Servo ON / OFF) · Safety Gantry (Suspended Start)

Sources

Electromagnetic brake - Wikipedia