stepper + encoder. resetting after stall

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15 Aug 2012 12:01 #23232 by strykerg
hi,

I have a stepper with an encoder on my lathe z axis. I managed to get the system to stop if a stall is detected (not the traditional way: I put axis-pos-fb and encoder-position through a near component which outputs to the axis' amp-fault).

my problem is when the axes stalls (or is moved when the amp is not enabled) there is no way to turn the system back on unless you manually move the axis until the encoder-position and axis-position are near eachother.

is there a way around this? I thought of resetting the encoder position to 0, then pass the encoder-position through a scale component and set the scale offset to the current axis-pos-fb. but i cant think of how to do this when the axis is turned on.

tried looking around but couldn't find detailed info on steppers + encoders

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15 Aug 2012 12:31 #23235 by andypugh
strykerg wrote:

is there a way around this?

You probably need to use a sample-hold function linked to machine-on to store the encoder counts and to subtract that latched value. (you might want to latch the difference, alternatively.
You might find that the "offset" function, (which specialises in lying about feedback) is useful too.
I think that sample-hold only works for S32 values, such as encoder counts. If you need to latch a float then you can use a mux2 looped-back on itself to do the same thing.

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15 Aug 2012 12:51 #23237 by strykerg
thanks for the info just what I needed to get started - didn't really know about these functions

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