Configuring scale feedback

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01 Jul 2010 08:00 #3257 by EFIUnlimited
My problem is, Axis has no provision for direct joint position feedback.

I have a stepper based milling machine with linear scales. If I pin the scale feedback to the motor position feedback, my screw comp gets added to it before it is interpreted as actual joint position. It also plays unusual games with homing. If I just subtract my joint actual position from my scale position, and feed the delta into the step gen, this works, but, when I disable the motors to use the machine manually, it doesn't keep track of the table properly.

What I need are a few new pins in axis.

axis.0.joint_pos_out
axis.0.joint_pos_in
axis.0.joint_pos_delta

By default, pos_out and pos_in should be net'ed together. This would work the same way as it currently does. In my case, I could disconnect these two, and feed my scale position into the pos_in pin. I could then feed the delta into the step gen, making a true dual feedback system. When I disable the motors, the table position would continue to track as I manually move the machine around.

Thoughts?

Brian

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