Mach-DSP User’s Manual
Document Number: MACH-DSP-9021
Page 48
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In general, this controls the acceleration that the scanner will experience, therefore
when greater speed is needed, this should be increased. Error-proportional (Servo) gain
is used in PD, PID and PDFF servo configurations.
Low Frequency Damping Gain
This controls the amount of velocity (derived through differentiated position) that is fed
into the summing node. Some servo drivers call this “Low Frequency Damping” or just
“Damping”. In general, this controls the deceleration that the scanner will experience,
therefore when overshoots are happening on steps of all amplitudes, increasing this
control may help. Low Frequency Damping Gain is used in all servo configurations (PD,
PID, PDF, and PDFF).
High Frequency Damping Gain
This controls the amount of velocity (derived through integrated current) that is fed into
the summing node. This works in a similar way to Low Frequency Damping Gain, but
the way that this servo term is derived, High Frequency Damping is typically applicable
only to fast-changing signals. If your application involves only slow-changing signals
(closed-loop bandwidths lower than around 2 kHz), High Frequency Damping Gain may
not be needed at all – in which case it can be left at zero. In other cases both Low
Frequency Damping Gain and High Frequency Damping Gain must be used (normally
not in equal proportions) to achieve critical damping. Thus, High Frequency Damping
Gain may be used in all servo configurations (PD, PID, PDF, and PDFF).
Integrating (Class 1) servo parameters
In this section, you will find additional parameters used by integrating servos, including
PID, PDF and PDFF servos.
Error Integral Gain
This controls the amount of integrated position error, which is fed into the summing
node. When this is set to zero (thus creating a Class 0 servo), a small amount of error
may remain when comparing the commanded position and actual position. When this is
set to a relatively low gain, position errors lasting more than a few milliseconds will be
minimized. When this is set to a relatively high gain, position errors can be reduced
more quickly, but this servo term must be increased slowly and carefully. Generally high
integrator gains also require high values of Position-proportional gain in order to
maintain stability.
Position-proportional gain
This controls the amount of position signal that is fed into the summing node. Generally
this should be left at zero for Class 0 servos, and will be higher (in many cases around
double) the Error Integral Gain setting.
