ADLINK PCI-8258 - Manual (Page 95)

Motion Control Theory 81
PCI-8254 / PCI-8258
(1) Data length :You may set up data length to determine number
of PID controller's gain value to be calculated by the program.
Gain values come out of PID controllers differ from each other as
a result of varied measurements and errors cause by other factors
despite they are of the same system and algorithm. A quantified
index is provided to validate the calculation results. Here the
average of PID controller gain values is displayed in the final value
window of MCP2 while its standard deviation is shown in MCP2's
Fluctuation window as the criteria for determining successful
calculation. Take example. If data length is set at 200, then the
program will calculate average and standard deviation (or change
rate) of 200 PID gain values. The calculation is set to be
completed with relative correctness in case the standard deviation
(or change rate) is smaller than 10%.
(2) Hysteresis :This setup is aimed at reducing the standard
deviation described earlier to unify outcome from each calculation
as consistent as possible. Take example. As shown in table below
the value of standard deviation declines with increasing Hysteresis
range. On the contrary, a PID controller with larger Hysteresis
ranges may lead to smaller system band and slower system
response as shown in table below. In either case it is ensured that
the controller can keep the system in specific performance range
as shown in table below where phase margin is equal to 60
degree.
(3) Sampling time : Set up sampling time of the encoder and may
affect the calculation outcome. Results of different sampling time
are given in table below where system bands are roughly the
same while the standard deviations are reduced and Phase
margin of 60 degrees remains complaint with system specification.
Hysteresis
KP gains
Standard
deviation (%)
KI gains
Standard
deviation (%)
KD gains
Standard
deviation (%)
Band width
(Hz)
Phase margin
(degree)
150 5.123 7.887 2.378 22 60
250 4.087 6.383 1.845 18.8 60
350 2.718 4.313 1.183 17.7 60
450 3.056 4.880 1.277 16.5 60
Sampling
time
KP gains
standard
deviation (%) KI gains
Standard
deviation (%) KD gains
Standard
deviation (%)
Band
width (Hz)
Phase
margin
(degree)
500 4.918 7.634 2.298 22 60
300 3.562 5.580 1.574 23.8 60
200 2.552 3.970 1.154 23.8 60
100 1.087 1.707 0.478 23.8 60