KEB COMBIVERT F5 Reference Manual page 296

Diagnostics and Troubleshooting
Problem
Encoder slippage/mounting
(PM motors)
296
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
generate torque. Performing a encoder/rotor position learn (LL05 SPI
or LL06 Encoder Pole Position Learn) determines a corresponding
encoder position offset value for a given rotor position. The encoder is
a mechanical 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
encoder 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 motor 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 mechanical relationship between the motor and encoder has
changed.
In most cases, encoder slippage has occurred or there is an
encoder 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 position.
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.