On 4/16/22 12:17, Torsten Curdt via Emc-developers wrote:
But this feedback loop decouples the real position from the meant-to-be
position. (expressed in the following error)
And I don't see how the real position could be reported back to LinuxCNC
so
it's still in full control of the movement.
...unless you connect the encoder directly to the Mesa instead of the
Closed Loop Stepper driver.
You can send the encoder feedback to lcnc as well as the drive using
splitter.
Ah, interesting.
The encoders on closed loop steppers seem to usually have 4 pins.
(EA+,EB+,EB-,EA-)
Does that mean it requires 4 inputs per motor? Or would this somehow be
normalized into STEPs and DIRs? Or what does LinuxCNC expect?
The +/- indicate a differential pair, for noise rejection.
The conversion to a single signal would be done in a
comparator IC at the input.
The splitting would not work for the servos that have the driver integrated
though.
For example JMC Servos can only provide feedback via modbus for example.
So I guess they wouldn't be really ideal to work with unless LinuxCNC could
also poll the modbus as a feedback channel.
It sounds like the ideal LinuxCNC setup would be a very dump driver
(without encoder support) and a stepper/servo with just an exposed encoder.
And then have LinuxCNC take care of everything.
But, then, you would be running blind, with no actual
position available at the computer.
This will work, of course, and is simpler, but you are
trusting the servo drives to ALWAYS have the machine at the
commanded position. The advantage of closing the loop in
the computer is that you can always graph the following
error to determine if the machine is accurately following
the G-code program.
Jon
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