Parker Aries AR-04CE - Servo Response Overview; Stability

Parker Hannifin
- 52 - Aries Controller Hardware Installation Guide
Even when the system is properly tuned, the position error can still be quite
significant due to a combination of factors such as the desired profile, the
motor's limitation, or the dynamic characteristics of the system. For example,
if the commanded velocity is higher than the maximum velocity the motor can
physically achieve, the actual position will always lag behind the commanded
position. Under these circumstances, a position error will accumulate no
matter how high the gains are set.
Servo Response Overview
Stability
The first objective of tuning is to stabilize the system. The formal definition of
system stability is when a bounded input is introduced to the system, the
output of the system is also bounded. What this means to a motion control
system is if the system is stable, and the position setpoint is a finite value,
the final actual position of the system is also a finite value.
In contrast, if the system is unstable, no matter how small the position
setpoint or how little a disturbance the system receives (such as motor
torque variation, load change, or noise from the feedback device), the
position error will increase exponentially in almost all cases. In practice,
when the system experiences instability, the actual position will oscillate in an
exponentially diverging fashion as shown in Table 27.
One commo
n misperception is that whenever there is oscillation, the system
is unstable. It is important to recognize that a system is considered stable if
the oscillation finally diminishes (damps out), even if it takes a long time.