US Patent 7401683 Elevator vibration damping apparatus and method

The present invention automatically detects the onset of instability of an elevator active ride control system and activates a system shutdown if it occurs. As an elevator car is guided along rails by guide elements, a plurality of sensors mounted on the car measure vibration transverse to a direction of travel. The signals from the sensors are input to a controller which in turn produces a controller output signal. This signal is used to energize an actuator positioned between the car and the guide elements and thereby dampen the vibrations acting on the car. As instability sets in, a controller signal increases. The controller signal is monitored by a comparator such that the actuator is deactivated if the controller signal becomes greater than a predetermined value.