Abstract: A locking device for a lift having an arm pivotably mounted for horizontal movement about a lifting carriage with two tubular members each pivotably connected at one end to the arm. One of the tubular members extends into a cylindrical housing and is locked thereto by balls mounted in ball cages urged by a spring to a locking position. The other tubular member is locked to the first tubular member by similar balls, cages and spring. A sleeve longitudinally slidably exterior to the two tubular members includes pins for engaging the ball cages to release the two tubular members.

Abstract: 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.