5-38 Operation MN1941WEN
5.9 Local servo axis - eliminating steady-state errors
In systems where precise and accurate positioning 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 drive
amplifier which may not be enough to overcome mechanical friction (this is particularly true in
current controlled systems). This error can be overcome by applying integral gain. The
integral gain, KINT, works by accumulating following error over time to produce a demand
sufficient to move the motor into the required position with zero following error. KINT can
therefore overcome errors caused by gravitational effects such as vertically moving linear
axes. With current controlled drive amplifiers a non-zero demand output is required to hold
the load in the correct position, to achieve zero following error.
Care is required when setting KINT since a high value will cause instability during moves.
A typical value for KINT would be 0.1. The effect of KINT should also be limited by setting the
integration limit, KINTLIMIT, to the smallest possible value that is sufficient to overcome
friction or static loads, for example 5. This will limit the contribution of the integral term to 5%
of the full demand output range.
1. Click in the KINT box and enter a small
starting value, for example 0.1.
2. Click in the KINTLIMIT box and enter a
value of 5.
With NextMove e100, the action of KINT and KINTLIMIT can be set to operate in various
modes:
Never - the KINT term is never applied
Always - the KINT term is always applied
Smart - the KINT term is only applied when the demand speed is zero or constant.
Steady State - the KINT term is only applied when the demand speed is zero.
This function can be selected using the KINTMODE drop down box.
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