Electrokinetica The Electro-mechanical Museum

Motor Room - Enter only with the authority of the Chief Engineer

1940s lift installation

'Vertical transportation' has always been an essential feature of high-rise developments and a welcome facility in any building. Electrically powered lift (elevator) installations have been providing this service for over a century but the machinery is normally unseen and unloved, locked away in a little room on top of the building. Here at ElectroKinetica we are taking the opportunity to reveal these powerful, reliable servants and explain some of the subtleties of their control systems.

The driving mechanism of most conventional lifts is quite straightforward and has changed little over the years; an electric motor rotates a large pulley termed a sheave, over which run the ropes suspending the car and its counterweight. The motor may drive the sheave directly or via a simple reduction gearbox, according to the speed and load capacity required. Because the car is propelled by the traction of the ropes on the sheave, these configurations are referred to as 'traction machines', either geared or gearless as appropriate. The car is held still by a spring-operated brake fitted to the motor shaft, which is released by an electromagnet when the motor is running. Many safety features are included to prevent the car running out of control, to prevent any doors or gates being opened until the car is correctly positioned at a floor and to prevent any movement until the doors or gates are securely locked. Most of these functions are carried out by electromechanical systems under the general supervision of a unit called the controller, which by contrast to the driving machine can be fiendishly complicated.

Early electric lifts used simple manual controllers, operated by a driver using a handle or rope from within the car. The driver was entirely responsible for choosing which floors to visit, stopping the car accurately level with the landing, and reconciling passengers' various requests as to which way to go next. The controller provided a means for the driver to start and stop the car smoothly, prevented it moving with the gates open, and ensured that the motor and brakes were not overstressed. In due course, automatic controllers were increasingly adopted as they dispensed with the need of a driver and allowed passengers to select their destination with pushbuttons instead. A sub-unit called the floor selector tracked the position of the car, and determined which direction the motor was to run in response to calls registered on the controller. Thus the controller took over the responsibility for dealing with calls in an efficient manner and co-ordinating other functions as they were introduced, such as automatic door-opening and interlinked working of multiple lifts. Electromechanical controllers had become complex pieces of equipment by the time they were superseded by electronic ones.

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