Elevator start control technique for reduced start jerk and acceleration

Abstract

Start jerk and acceleration overshoot on elevator starting are reduced by bypassing and delaying application of an elevator closed loop velocity control system. A bypassing starting torque increases the torque of the motor before the onset of motion, at which time the starting torque is leveled off and held constant and the velocity speed reference profile is started. A small creep velocity dictation injected into the closed velocity loop in addition to the starting torque command causes the difference between the speed profile and the sensed speed to be very small during starting. Moreover, by selecting lift brake current in such a way as to promote a smooth brake opening and by selecting an increasing starting torque profile which overcomes the declining brake torque just after the brake begins to open, the torque needed to compensate for the load can be evenly balanced with the release of brake torque. The timing of initiation of the starting torque may be selected according to a time delay which may vary between different installations and be adjustable in order to obtain zero rollback when the elevator car first moves. A step decrease in the starting torque may be dictated upon detecting system movement in order to compensate for the transition from static friction to sliding friction. The rate of increase of starting torque is preferably exponential.