MN1957 Operation 5-29
www.baldormotion.com
5.9 Servo axis - eliminating steady-state errors
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 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 ESB-2, 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.
Servo Systems Co. • 115 Main Road • P.O. Box 97 • Montville, NJ,
07045-0097 • (973) 335-1007 • Toll Free: (800) 922-1103
Fax: (973) 335-1661 • www.servosystems.com
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