Recalibrating an elevator load measuring system

Abstract

Elevator load is computed from sensors. These sensors provide load signals. The load, defined by a stored load equation, is the product of those signals and a gain signal summed with an offset signal. Load computation using those signals is augmented by a recalibration routine. The routine to adjust the offset is initiated when the car transits floors in an empty car condition. Current equation offset and the latest empty car signal levels are compared. If the difference is less than a value the last levels become the offset; if not the equation offset is incremented changed. Load computation is further augmented by sensing car rollback, to augment the gain signal. Rollback may occur after the brake holding the car in position is lifted but before a speed dictation signal is given to the motor, causing the car to move if motor torque is not matched to the load as computed from the load equation. Depending on the magnitude of the rollback, the gain is increased or decreased in increments through successive elevator stops at floors provided there is sufficient passenger (cab) load. Rollback not caused by incorrect motor pretorquing when the brake is lifted is discarded by comparing the actual change in position of the car with the change in motor shaft or sheave position.