| 摘要 |
A lifting apparatus of the type having a number of columns supporting a load platform each column driven by an electrical, polyphase current motor whereby sensors on each column, for example potentiometers, produce a signal indicating the height of that column. The signals are applied to a comparator which in turn provides an output to one or more electronic switches, such as a triac or thyristor having a diode connected in parallel with it for conducting current in an opposite direction, each such switch connected to a winding of a motor to control the current applied so as to reduce any difference in height among the columns. |
