ADLINK PCI-8158 - Manual (Page 85)

Operation Theory 75
4.5.1 Command position counter
The command position counter is a 28-bit binary up/down counter.
Its input source is the output pulses from the motion controller. It
provides the information of the current command position. It is
useful for debugging the motion system.
Our motion system is an open loop type. The motor driver receives
pulses from motion controller and drive the motor to move. When
the driver is not moving, it can check this command counter and
see if there is an update value on it. If it is, it means that the pulses
have seen sent and the problem could be on the motor driver. Try
to check motor driver’s pulse receiving counter when this situation
is happened.
The unit of command counter is in pulse. The counter value could
be reset by a counter clear signal or home function completion.
Users can also use a software command counter setting function
to reset it.
4.5.2 Feedback position counter
The feedback position counter is a 28-bit binary up/down counter.
Its input source is the input pulses from the EA/EB pins. It counts
the motor position from motor’s encoder output. This counter
could be set from a source of command position for an option
when no external encoder inputs.
The command output pulses and feedback input pulses will not
always be the same ratio in mini-meters. Users must set the ratio if
these two pulses are not 1:1.
Because our motion controller is not a closed-loop type, the feed-
back position counter is just for reference after motion is moving.
The position closed-loop is done by servo motor driver. If the servo
driver is well tuned and the mechanical parts are well assembled,
the total position error will remain in acceptable range after motion
command is finished.
4.5.3 Command and Feedback error counter
The command and feedback error counter is used to calculate the
error between the command position and the feedback position.