Download MS332 Operation Manual - Electro

Index-Follower Mode
Description:
Input Hardware:
- Index-Follower mode uses lead and follower quadrature-output incremental encoders and lead and follower index
pulse devices. An Index pulse signal is usually triggered by an event such as an object passing by a proximity
sensor.
Operation:
- Index-follower mode controls follower motor speed, causing the feedback encoder to follow the lead encoder
according to the rpm ratio while simultaneously positioning feedback index pulses relative to lead index pulses
according to the index phase set-point.
- When using a bidirectional drive and motor, the feedback encoder follows the lead encoder in either direction
(forward or reverse).
The connections to the MS332 lead and feedback encoder inputs, and lead and feedback index inputs are as shown
in the following diagram:
INDEX - FOLLOWER CONTROLLED APPLICATION
LEAD ENCODER SIGNAL
LEAD INDEX PULSE SIGNAL
INDEX DEVICE
M
RUN/STOP
SWITCH
GROUND C
ANALOG
OUTPUT
CLOSED LOOP /
OPEN LOOP
SWITCH
MASTER
CONTROLLED
PROCESS
MS332 IN
INDEX-FOLLOWER
MODE
VARIABLE
SPEED
DRIVE
M
INDEX FOLLOWER
CONTROLLED
PROCESS
QUADRATURE
ENCODER
QUADRATURE
ENCODER
INDEX DEVICE
FEEDBACK INDEX PULSE SIGNAL
FOLLOWER FEEDBACK ENCODER SIGNAL
Control Theory:
Index Phasing:
- Index phase corrections position the effective feedback index pulses relative to the effective lead index pulses
according to the Index Phase set-point. In this way, a periodic feedback-process event may be precisely phased to
precede, coincide with, or follow a periodic lead-process event by a desired number of feedback encoder pulses.
Index phase corrections occur immediately after each effective feedback index pulse.
RPM Ratio:
- Between index phase corrections, feedback encoder speed is controlled by forcing the number of feedback
encoder pulses received (in time T) equal to the expected number determined by the lead encoder pulses received
(in time T) and certain user variables (see formula below). No pulses are gained or lost between index phase
corrections: the cumulative error is zero. Therefore if either index pulse source were to fail, index phase
corrections would cease but the follower-to-lead phase relationship would not change.
- This closed-loop pulse-meshing algorithm is similar to that of Ratio-Follower mode. However, unlike
Ratio-Follower mode, the RPM ratio derives from a feedback to lead index pulse matching ratio
(Var01.10/Var01.11) and not from the set-point. The Index-Follower mode feedback/lead RPM ratio formula is
shown here:
FbRPM / LdRPM = (FbPPI / LdPPI) * (Var01.05 / Var01.02) * (Var01.10 / Var01.11)
Desc. Oper. Mode Sect. page - 3
(bA02.XX)
(101801)