KEB COMBIVERT F5 Operation Manual page 114

Operation Problems
Problem
Encoder slippage/mounting
(PM motors)
114
Cause/Solution/Troubleshoot
The position of the rotor must be known for synchronous (PM) motors
for the drive to properly commutate the stator magnetic field and gener-
ate torque. Performing a encoder/rotor position learn (LL05 SPI or LL06
Encoder Pole Position Learn) determines a corresponding encoder po-
sition offset value for a given rotor position. The encoder is a mechani-
cal extension of the rotor and therefore acts as an electrical commutator.
If the mechanical relationship (eg. mounting) between the motor and
encoder changes (eg. slippage), the position information from the en-
coder does not accurately reflect the actual rotor position resulting in the
actual commutation angle being incorrect.
When the commutation angle is not correct, more current is required to
produce a given amount of torque. Large enough changes will result in
very high current draw and low torque production. This leads to the mo-
tor being unable to move (stalling) or unable to hold the load (movement
in direction of load, eg. empty car counter weights pull car up). In this
case, the current is often reaching the corresponding LC30 Maximum
Torque limit or the peak current rating of the drive,
If the encoder/rotor position is re-learned and determined to be
different than the previous value of the LE06 Encoder Pole Position
by more than 2,000 counts, then this is a clear indication that the me-
chanical relationship between the motor and encoder has changed.
In most cases, encoder slippage has occurred or there is an en-
coder mounting issue. The accumulation of slippage may occur over
distance (between a few inches to the entire hoistwaydistance), over
time (sometimes after several years of operation), or from a change in
direction (sometimes due to loose encoder mounting).
The suggested course of action is to first inspect the encoder mounting
(in many cases, the encoder may actually be mounted tight), remove
the encoder and inspect again, and re-install the encoder then relearn
the encoder position. If issues persist, re-learn the encoder/rotor posi-
tion. If large difference between learns persist (it is important to move
car between learns to accumulate slippage, if this is the issue), continue
to inspect the motor and encoder for mounting issues, or replace the
encoder as a last resort.