Importance

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Abstract

A hydraulic elevator includes level sensors for establishing dead zones of different sizes and for changing the dead zone while the car is stopped at a floor. A controller selects the size of the dead zone, for purposes of relevel operations, based upon elevator operating state (e.g. doors open or closed, time of day, time since last run) or other parameters (excess oil temperature, motor temperature, or excess motor starts). The controller also selects an effective hysteresis value either to return the car to floor level or to move the car to a position above floor level. In this manner, the controller maintains a small dead zone, and returns the car to level, when the doors are open. When the doors are closed, a larger dead zone is selected to reduce the frequency of relevel operations. Moreover, under certain conditions, the car is moved, during releveling, to a position above the landing, to further reduce the number of required relevel operations over time.

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First Claim