ElmoMC SimplIQ Digital Servo Drives-Bell Command Reference - Manual (Page 295)

The reference to the speed controller is composed of the derivative of the position
command (speed) and of the output of the position controller. The derivative of the
position command is multiplied by the FF[2] . Normally FF[2] matches the units
between the position and the speed controllers. For UM=4, FF[2] equals the gear ratio
between the speed sensor and the position sensor. For UM=5, the speed feedback is
derived from the position sensor, so normally FF[2]=1.
You can use the gain scheduler, or the gains of the controller can be fixed by setting
GS[2]=0.
Using the high-order filter is optional. To disable the high-order filter, set KV[48]=0.
The high order filter has no units and its DC gain is always unity. For more details,
refer to the chapter on
Filters .
The position controller throws exceptions on excessive position errors (ER[3]), and on
deviation of the feedback position from its limits LL[3], HL[3].
The gain scheduling is derived from the speed reference + GS[10] x [Position
error]. This means that for position control, the gain scheduling does depend on the
feedback – otherwise the feedback will become too sluggish at low speeds.
8.3.2 Position Controller Parameters
The position controller drives an inner speed controller.
The position controller is made of a non-linear gain and an optional filter.
Most of the applications use the gain only.
The position controller calculates the position error:
) ( ) ( ) ( t k PosFeedbac t PosCommand t e
POS
− = [counts]
then it calculates a linear gain:
1 p POS
x K e
= ⋅
and a non-linear gain:
2
2 [9]
POS
x GS e
= ⋅ ⋅
and takes
1 2
min( , ) ( )
pos
x x x sign e
=
The parameter GS[9] is the maximum deceleration that the motor can drive. This
assures, on one hand, that for small position errors the position controller is linear,
whereas for larger position errors, the position controller will never require a speed
that can't be stopped without overshooting.
SimplIQ for Steppers Application Note The Position and Speed Controller
MAN-STECR (Ver. 1.1)
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