Mach-DSP User’s Manual
Document Number: MACH-DSP-9021
Page 85
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Indeed, by integrating position error over time, and amplifying that and having it drive
the motor, the position error will go to zero
eventually
. However, adding even this small
amount of integration to the servo loop has caused the mirror to actually overshoot the
intended command position, and this overshoot remains for more than 6 milliseconds!
This happens because for approximately 350 microseconds, there was a large position
error (4 degree error in the beginning of the step). This large error caused a large
amount of accumulation by the integrator. This large accumulated error becomes
amplified by the servo, ultimately causing an overshoot.
However, this problem can be largely solved by adding an additional servo term. To
prepare to adjust that servo term, use the Oscilloscope in the Mach-DSP program, and
set Channel D to show the Integrated Error, and set the Integrated Error scale factor to
0.8
Once the Oscilloscope is setup as described above, adjust the Position-proportional
gain to 5. You will observe that the Position Error is no longer overshooting the intended
target. However, you will also notice that a small amount of overshoot and ringing has
crept into the position (and error) signal – as if you had increased the Servo Gain
control. This occurs because Error Integral and Position-proportional gains are very
