If you use a standard stop command the accuracy is
determined by the internal task time. That is not the case
when you use the precise stop function; it eliminates the task
time dependence and increases the accuracy substantially.
The adjustable frequency drive tolerance is normally given
by its task time. However, by using its special precise stop
function the tolerance is independent of the task time
because the stop signal immediately interrupts the
execution of the adjustable frequency drive program. The
precise stop function gives a highly reproducible delay from
the stop signal is given until the ramping down starts. A test
must be done to find this delay as it is a sum of sensor, PLC,
adjustable frequency drive and mechanical parts.
To ensure optimum accuracy, there should be at least 10
cycles during ramping down, see 3-42 Ramp 1 Ramp-down
Time, 3-52 Ramp 2 Ramp-down Time, 3-62 Ramp 3 Ramp-down
Time and 3-72 Ramp 4 Ramp-down Time .
The precise stop function is set up here and enabled from DI
T29 or T33.
1-83 Precise Stop Function
Option: Function:
[0]
*
Precise
ramp stop
Only optimal when the operational speed of, for
example, the conveyor belt is constant. This is an
open-loop control. Achieves high repetitive
precision at the stopping point.
[1] Cnt stop
with reset
Counts the number of pulses, typically from an
encoder and generates a stop signal after a pre-
programmed number of pulses - 1-84 Precise Stop
Counter Value - has been received at T29 or T33
[30].
This is a direct feedback with one-way closed-loop
control.
The counter function is activated (starts timing) at
the edge of the start signal (when it changes from
stop to start). After each precise stop, the number
of pulses counted during ramp-down to 0 rpm is
reset.
[2] Cnt stop
w/o reset
Same as [1] but the number of pulses counted
during ramp-down to 0 rpm is deducted from the
counter value entered in 1-84 Precise Stop Counter
Value.
You can for example use this reset function to
compensate for the extra distance done during
ramping down and to reduce the impacts of
gradual wear of mechanical parts.
[3] Speed
comp
stop
Stops at precisely the same point, regardless of
the present speed, the stop signal is delayed
internally when the present speed is lower than
the maximum speed (set in 4-19 Max Output
Frequency).
The delay is calculated on the basis of the
reference speed of the adjustable frequency drive
1-83 Precise Stop Function
Option: Function:
and not on the basis of the actual speed.
Therefore make sure that the adjustable
frequency drive has ramped up before you
activate the speed compensated stop.
[4] Com cnt
stop w/rst
Same as [3] but after each precise stop, the
number of pulses counted during ramp-down to 0
rpm is reset.
[5] Comp cnt
stop w/o r
Same as [3] but the number of pulses counted
during ramp-down to 0 rpm is deducted from the
counter value entered in 1-84 Precise Stop Counter
Value.
You can for example use this reset function to
compensate for the extra distance done during
ramping down and to reduce the impacts of
gradual wear of mechanical parts.
This parameter cannot be adjusted while the motor is
running.
1-84 Precise Stop Counter Value
Range: Function:
100000
*
[0 - 999999999 ] Enter the counter value to be used in
the integrated precise stop function,
1-83 Precise Stop Function.
The maximum permissible frequency
at terminal 29 or 33 is 110 kHz.
Not used for selection [0] and [3] in
1-83 Precise Stop Function
1-85 Precise Stop Speed Compensation Delay
Range: Function:
10 ms
*
[0 - 100
ms]
Enter the delay time for sensors, PLCs, etc. for
use in 1-83 Precise Stop Function. In speed
compensated stop mode, the delay time at
different frequencies has a major influence on
the stop function.
Not used for selection [0], [1] and [2] in
1-83 Precise Stop Function
Parameter Descriptions FC 300 Programming Guide
MG.33.MA.22 - VLT
®
is a registered Danfoss trademark 3-23
3
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