Baldor MN1274 06/2001 installation manual

In summary, the following rules can be used as a guide:

HKPROP: Increasing KPROP will speed up the response and reduce the effect of disturbances and load variations. The side effect of increasing KPROP is that it also increases the overshoot, and if set too high it will cause the system to become unstable. The aim is to set the Proportional gain as high as possible without getting overshoot, instability or hunting on an encoder edge when stationary (the motor will buzz).

HKVEL: This gain has a damping effect, and can be increased to reduce any overshoot. If KVEL becomes too large it will amplify any noise on the velocity measurement and introduce oscillations.

HKINT: This gain has a de-stabilizing effect, but a small amount can be used to reduce any steady state errors. By default, KINTMODE is set so that the KINT term is ignored.

HKINTLIMIT: The integration limit determines the maximum value of the effect of integral action. This is specified as a percentage of the full scale demand.

HKVELFF: This is a feed forward term and as such has a different effect on the servo system than the previous gains. KVELFF is outside the closed loop and therefore does not have an effect on system stability. This gain allows a faster response to demand speed changes with lower following errors, for example you would increase KVELFF to reduce the following error during the slew section of a trapezoidal move. The trapezoidal test move can be used to fine-tune this gain.

HKDERIV: This gain has a damping effect. The Derivative action has the same effect as the velocity feedback if the velocity feedback and feedforward terms are equal, but scaled by a factor of 16.

In systems where precise positioning accuracy is required, it is often necessary to position within one encoder count. Proportional gain, KPROP, is not normally able to achieve this because a very small following error will only produce a small demand for the amplifier which may not be enough to overcome mechanical friction (this is particularly so for current controlled systems). This error can be overcome by applying some Integral gain.

The Integral gain, KINT, works by accumulating following error over time to produce a demand sufficient to move the motor into the zero following error position. KINT can therefore also overcome errors caused by gravitational effects, such as vertically moving linear tables, where with current controlled drives a non-zero demand output is required to achieve zero following error.

For further details see Appendix A.

*The 1ms sampling interval can be changed using the LOOPTIME keyword.

55