Torque, speed and position control

Many applications exist where something has to be controlled to follow a reference quantity. For example, the speed of a large motor may be set from a low-power control signal. This can be achieved using a variable-speed drive. Ideally, the relationship between the reference and the motor speed should be linear, and the speed should change instantly with changes in the reference. Any control system, with an input reference signal, a transfer function F and an output. For the system to be ideal, the transfer function F would be a simple constant, so that the output would be proportional to the reference with no delay.