In the field of automation, a motion control system consists of
mechanical hardware coupled to a prime mover, the operation of which is
governed by a computerized controller that compares the command position
to the indicated load position. Typically, the indicated load position
comes from a rotary shaft encoder or linear position encoder. In
response to a difference between the command position and indicated load
position, the controller generates a drive signal that is fed to the
device that regulates the speed and direction of the prime mover — for
example, an electronic amplifier driving a servomotor.
This
process of reading position, comparing it to the command position, and
then driving the prime mover until it is positioned correctly is called
closed-loop motion control. Besides position, other controlled variables
such as velocity (the mathematical derivative of position) or force can
also be measured. With respect to position and velocity, the accuracy
of the controlled motion – from the perspective of the load — is highly
dependent upon how closely the indicated load position matches actual,
real-world load position. The indicated position is always a facsimile
of the actual load position. Due to various error-inducing factors, the
indicated load position never exactly matches the actual load position.
The nature of the induced position errors depends on the architecture of
the position encoder and how it interacts with mechanical drive
hardware. |
