TUNING THE CONTROL LOOPS 6-27
SB1391 Hardware and Setup Guide - Document revision no. 1.14
6.9.1. Dual Loop Control - Implementation
Encoder 1 (ENC1), which is mounted on the motor axis, is used to close the velocity loop (and
also, in the case of a brushless motor, for software commutation).
Encoder 2 (ENC2), which is mounted on the load (the position that is being controlled) is used to
closed the position loop.
The parameter $CU ($ stands for the axis, i.e., "x," "y," etc,), which defines the type of
commutation feedback device, is also used as the switch for dual loop control. Bit 2 of $CU must
be always be set to 1 when dual loop control is used.
$CU value (decimal) Feedback device(s) and type of control
$CU = 2
Encoder (no Hall), single loop, for a DC brush, DC brushless (AC
servo/AC synchronous), or AC induction motor
$CU = 3
Encoder + Hall, single loop, for a DC brushless (AC servo/AC
synchronous) motor.
$CU = 6
Encoder (no Hall), dual loop, for a DC brush, DC brushless (AC
servo/AC synchronous), or AC induction motor.
$CU = 7
Encoder + Hall, dual loop, for a brushless or AC induction motor.
$D21, $D22 from the D array are used for velocity scaling.
$D22 is determined from the maximum velocity of the motor for the application.
$D21 is determined from the maximum velocity of the load for the application.
D22 =
VMm
6
10500 ×
Where
VMm - Max velocity of the motor (counts/sec).
D21 =
()
()
resENC2
resENC1D22
×
Where
ENC1(res) - Number of counts of ENC1 per motor revolution (
LF
2LR × ).
ENC2(res) - Number of counts of ENC2 per motor revolution.
The position loop bandwidth [Hz] (Fc) is computed as follows:
Fc (position) =
21
20000
2
2
1
D
GA
GF
×××
π
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