Ward Leonard control

In the early 1900s, the control system of Ward Leonard was adopted by the U.S. Navy and also used in passenger lifts of large mines.

It also provided a solution to a moving sidewalk at the Paris Exposition of 1900, where many others had failed to operate properly.

Connected to automatic anti-aircraft gun directors, the tracking motion in two dimensions had to be extremely smooth and precise.

The MIT Radiation Laboratory selected Ward-Leonard to equip the famous radar SCR-584 in 1942.

[1] The key feature of the Ward Leonard control system is the ability to smoothly vary the speed of a DC motor, including reversing it, by controlling the field and hence the output voltage of a DC generator, as well as the field of the motor itself.

This 'prime mover' could be an AC motor, or it could be an internal combustion engine (its application to vehicles was patented by H.W.

A Ward Leonard drive can be viewed as a high-power amplifier in the multi-kilowatt range, built from rotating electrical machinery.

Where the 'prime mover' is electrical, a Ward Leonard drive unit consists of a motor and generator with shafts coupled together.

It effectively decouples intermittent short-term high loading of the generator from the AC supply.