Omron CP1L - 12-2007, Operation Manual

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Inverter Positioning
Section 5-3
7. When a speed command is sent to the inverter, the motor will turn at the
command speed and feedback pulses (i.e., the amount of movement) from
the encoder will be returned to a high-speed counter of the CP1L. The
CP1L will continue to send a speed command to the inverter until the error
counter (i.e., the position error) goes to zero, i.e., until positioning has been
completed.
8. When the error counter goes to zero, the speed command to the inverter
will also go to zero. Even after the completion of internal pulse output (i.e.,
position command) from the pulse output instruction, the CP1L will main-
tain the error counter so that is remains at zero.
9. The status of the error counter (such as the command direction and in-po-
sition status) will be stored in the Auxiliary Area. This status can be read
from the user program to enable controlling output of commands to the in-
verter.
For example, if a change in the load causes the motor shaft to turn, feedback
pulses from the encoder will enter the error counter, the value in the error
counter will be reduced, and the Reverse Command Flag in the Auxiliary Area
will turn ON. By writing the ladder program to output a reverse operation com-
mand to the inverter for the Reverse Command Flag, a command in the oppo-
site direction of motor shaft movement will be output from the CP1L to the
inverter, causing the motor to return to its original position. This compensating
operation to continuously maintain the current stop position is called a servo
lock.
Other Functions
Servo Locks with Vector
Control Inverters The servo lock on an inverter can be used to stop positioning. By using the
inverter’s servo lock, the inverter positioning function and the output command
to the inverter can be stopped from the user program without using feedback
control even if the error counter value is not zero. This enables servo locks
when using an inverter with vector control.
Clearing the Error Counter
for Errors If the motor shaft is moved manually for error stops or when the inverter is
stopped, feedback pulses will accumulate in the error counter. This can be
very dangerous because it may cause the motor to suddenly return to the
original position at high speed when operation is started again. To prevent
such problems, an error counter error output can be produced when more
than a set number of pulses accumulated in the error counter when position-
ing operations are stopped.