An unintended car movement protection device that detects and stops inadvertent car motion away from a landing with the doors open, as required by EN 81-20.
Full Definition
The Unintended Car Movement (UCM) protection device is a mandatory safety feature introduced in EN 81-20 clause 5.6.7 (previously covered by EN 81-1 amendment A3). It detects movement of the car away from a landing while the landing or car door is open — a condition that can trap or injure passengers stepping in or out. The system must detect a movement exceeding 1.2 m/s or a displacement greater than 0.2 m (rising car) or 0.12 m (descending car). On detection, the device must bring the car to a stop and prevent it from restarting until manually reset by a competent person. The UCM function can be implemented by: monitoring the rope or car position with redundant encoders; a dedicated safety relay module; an integrated Safe Torque Off (STO) function in a SIL-rated frequency converter; or a hydraulic check valve on hydraulic lifts. The stopping device may use the drive motor brakes, safety gear, or a separate clamping device on the guide rails. The complete UCM safety chain must achieve at minimum Category 3, Performance Level d (PLd) per EN ISO 13849-1.
