Velocity regulated, open current loop, variable voltage, variabl

Elevator – industrial lift truck – or stationary lift for vehicle – With barrier for regulating access to load support – Includes motor or motor driven linkage for shifting barrier

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187287, 318466, 318811, B66B 1314

Patent

active

055095046

ABSTRACT:
An elevator car door is moved by a variable voltage, variable frequency linear induction motor which is driven open current loop to achieve a desired velocity profile indicated by an incremental linear encoder, with washed out proportional and integral gain. A magnetizing current insufficient to overcome the weight of the door is added in quadrature with the linear force current, and frequency is determined open loop in a predetermined fashion. Pulse width modulation voltage control signals are utilized to apply fixed voltages of correct polarity through a low pass three phase filter to the windings of the motor for correct intervals of time so as to synthesize desired sinusoidal winding currents. A boost of current is provided following each zero crossing of the sinusoidal winding currents to overcome lags therein. A ramp down of voltage avoids dropping the door at the end of door opening and door closing.

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patent: 5400240 (1995-03-01), Araki

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