ADLINK PCI-8258 - Manual (Page 89)

Motion Control Theory 75
PCI-8254 / PCI-8258
4.2 Closed-loop Control
4.2.1 Close-loop Control Overview
The close-loop control system works like this: after a command is
sent, a group of sensors get system output signals during motion
process and returned to the controller, a error signal then can
derived by comparing the original command against the feedback
signal which is then returned to controller. As the controller
structure is designed on the basis of pre-defined System Dynamic,
the deviation signal received by the controller will be combined
into a brake signal and feed into the brake to reduce deviations
and external interruptions and noises such that system output may
comply with given commands gradually.
In general, commonly adopted controllers by the manufacturing
industries are of PID controller on account of its simple structure
and its capabilities in meeting most industrial control requirements.
Thanks to its PID+ velocity and acceleration feed forward design,
this controller provides much improved overall control
performance with servo update rate up to 20KHz.
Below we first discuss the PID controller, a continuous-time
standard PID controller mathematical form
where is the combined control amount of Proportional
control, Integral control, and Derivative control, the gain,
the integral time constant, and the derivative time constant.
Impact of each control item on system performance is described
below.
a Proportional Control
As Time-domain is concerned, more Proportional gain may speed
up responses as the system bandwidth increases with that of
Frequency-domain at the expense of Stability. This makes the
system prone to vibration as Gain margin decreases. Another
important function of proportional control is to reduce Steady-state
error.
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