ADLINK Technology cPCI-8168, User Manual

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Operation Theory 73
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
informs the user of the current command position and is useful for
debugging the motion system.
The cPCI-8168 is an open loop type motion controller. The motor
driver receives pulses from motion controller. When the driver is
not moving, we can check this command counter and see if there
is an updated value. If it is, it means that the pulses have seen
sent and the problem could be on the motor driver. In this situation
the motor driver’s pulse receiving counter should be checked.
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 command position when there are 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.
Since the cPCI-8168 is not a closed-loop type motion controller
the feedback position counter is just for reference after motion
begins. The position closed-loop is done by the servo motor driver.
If the servo driver is well tuned and the mechnical parts are well
assembled, the total position error will remain in an acceptable
range after the motion command is finished.