Pololu Jrk USB - Manual (Page 43)

4. Note how close your system gets to an error of zero using just the
proportional term. You can use the integral term to get it much lower:
with the integral limit set at 1000, try increasing the Integral Coefficient
until you see a correction that brings the error closer to zero. In the plot
window shown here, you can see that the proportional term gets the error
down to about 10, then the integral term builds up and, half a second
later, moves the motor just a bit, reducing the error to ±1.
5. For systems that have a lot of friction relative to external forces,
enable a Feedback dead zone so that the integral term doesn’t cause a
slow oscillation very close to an error of zero. Watch how the integral
term and duty cycle build up over time to achieve. this. The plot was created with a dead zone of 4; without this,
the integral term would have continued to build up, but at a slower rate, after the first adjustment.
6. Enable the Reset integral when proportional term exceeds max duty cycle option to prevent the integral from
winding up during large motions. This is also shown in the plot: the integral term does not start increasing until
the error is close to zero.
7. Have your system take large steps (for example, by clicking the bar
area of the Input tab scrollbar to move the target by 200) and use the
graph to examine whether it consistently overshoots (crosses zero before
coming to a stop and moving back) or undershoots (does not reach zero
before slowing down). The plot window shown here, drawn for a system
using a Derivative Coefficient of zero, shows clear overshooting. In this
example, the error actually oscillates back and forth several times before
settling down.
8. Increase the Derivative Coefficient to get rid of any overshooting,
but not so much that it undershoots. The plot window shown here
demonstrates undershooting, using a Derivative Coefficient of 10. You
can see that the error never reaches zero. Instead, it gradually approaches
zero after each step.
9. Experiment with your system. Adjust any parameters as necessary to
get the behavior that you need.
The following example plot shows a well-tuned system, with Proportional,
Integral, and Derivative Coefficients of 6.0, 0.25, and 7.5. When taking
steps, the system stops very quickly at a position with very small error, randomly overshooting or undershooting by a
small amount.
Pololu Jrk USB Motor Controller User's Guide © 2001–2014 Pololu Corporation
5. Setting Up Your System Page 43 of 45