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4. CONTROL OF VIX DRIVES 91
Stall Detection
Stall detection is only possible if an encoder is fitted to the motor or load. A stall is reported
when the error between the commanded position and the actual position, determined by the
encoder, exceeds the value set in the error window of the STALL command.
Stall Detection Set-up
A stall condition is signalled when the number of expected stall-encoder steps does not
match the number of steps received. During a move the indexer constantly monitors any
build-up of stall error, and once the difference exceeds a programmed error window, a stall
condition is reported. Note, the stall error count is reset following an ON, STALL, GH or G
command.
Set system variable EM to equal the number of stall encoder counts per rev. This allows the
use of a low resolution stall-detect encoder without effecting the motor positioning resolution
(as set in the motor command). However, if LOADENC is enabled the positioning resolution
is now determined by EM as distance is commanded in stall encoder steps.
The error window size needs to be large enough to detect a single de-synchronisation of the
motor which is the equivalent of one rotor tooth or 4 full steps (7.2 degrees). Allowing for the
normal lag and lead occurring during acceleration and deceleration, of up to 3.6 degrees, an
overall error window of 5 degrees should be set - 14 steps with a 250-line encoder. The
error window is measured in motor steps with LOADENC and SCALE disabled, load steps
with LOADENC enabled, and user steps with SCALE enabled.
Fault on Stall
When STALL is enabled (on/off parameter set to a 1), and mode is set to 1 (run fault) motion
is stopped if the error between the commanded position and the actual position exceeds the
error window value. If a fault label is defined for this condition a fault will be reported and
can be identified by reading the status bits.
Output
Any one of the drive’s outputs 1 to 3 can be turned ON when a stall condition is detected.
This command option allows a stall to be signalled externally by lighting a lamp or LED.