Hypertherm HTA Rev 6.00 Install Guide - Manual (Page 117)

Appendix A: Motion Overview 105
motion test of the system and does not use gain terms or the position loop for motion. Please refer to
the Installation Guide provide with your control for more information on this feature.
3) Gain Term Definitions
Proportional Gain
In a feedback control system the error term is acted on by the control system and it in turn alters the
output. Proportional Gain is pure amplification of the error term. In a closed loop control system this is
proportional to the error signal. Simply put, the output is Proportional Gain times error.
In most systems Proportional Gain this is the primary tuning parameter to improve the response of
the position loop.
Integral Gain
Perhaps the best understanding comes from realizing that the limit of Proportional Gain is that it
cannot completely eliminate error. The system can become unstable if only Proportional Gain is used
to try and eliminate all the error in a system. When the response of a system is considered
satisfactory, but steady state error is excessive, the error can be further reduced by increasing
system gain only for long term accumulations of error over time. Integral gain is sometimes used to
compensate for static load disturbances like torque loading, gravity bias, and offset.
NOTE: This term can cause instability in a system as it has a more instant effect at the beginning of a
move profile. Therefore. it is rarely used in the types of control systems presented here. Only small
adjustments to Integral Gain should be made if indications of steady state error exist. In almost all
applications this value is set to zero. We recommend using the Feed Forward Gain for closing
following error occurring during a move profile.
Derivative Gain
Derivative Gain responds to the rate of change of the signal and can produce corrections before the
error term becomes large, therefore it is useful in improving the transient response of a system.
Since it opposes change in the controlled output, it can produce a stabilizing effect by damping a
tendency toward oscillation. This is the reason we promote tuning by following error to the maximum
Proportional Gain then setting Derivative Gain at 10% of Proportional Gain as a rule of thumb. Do not
overdo Derivative Gain as it can have a detrimental effect on the overall response of the system.
Feed Forward
Acts to “push” the commanded output ahead to reduce or eliminate dynamic following error. Where
dynamic following error is defined as the difference in actual position to commanded position that
exists during motion. It is a more pure term than integral gain. It could be defined as the ability to
correct for a “lag” in the system with an effect similar to Proportional Gain. Do not increase feed
forward gain to the extreme as it can result in positive following error and excessive overshoot.