Following Error When Homing

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21 Apr 2020 13:03 #164958 by rmu
Replied by rmu on topic Following Error When Homing
Hal file:

File Attachment:

File Name: Biesse_Rover_342.hal
File Size:11 KB


Encoder resolution on X and Y scales is a bit on the course side, 125 pulses per mm on X and 250 pulses per mm on Y. Z has 800 pulses per mm.
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21 Apr 2020 13:36 #164962 by PCW
Replied by PCW on topic Following Error When Homing
That looks normal function order wise

could you try with

setp pid.x.error-previous-target false
(this will change the tuning)

Otherwise to chase this down will probably require halscope
and a wide following error setting so a following error is not tripped

Then trace the position, following error, PID out and index enable at
say 2 servo thread periods per division when homing (single trace triggered on
index enable falling edge)

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22 Apr 2020 07:30 #165052 by rmu
Replied by rmu on topic Following Error When Homing
This is a Heisenbug. As soon as i attach the HalScope, those axis/joints I watch do work as supposed.

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22 Apr 2020 07:56 - 22 Apr 2020 08:04 #165055 by rmu
Replied by rmu on topic Following Error When Homing
Got it. Don't know what to make of it. Following error explodes one servo period after index-enable is 0. Second screenshot is from second attempt, when it works. x-pos-cmd when zoomed in looks exactly like f-error.
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Last edit: 22 Apr 2020 08:04 by rmu. Reason: Add second screenshot.

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22 Apr 2020 12:03 #165082 by tommylight
Those screenshots point to axis not being tuned properly.

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22 Apr 2020 12:28 - 22 Apr 2020 12:30 #165092 by rmu
Replied by rmu on topic Following Error When Homing

tommylight wrote: Those screenshots point to axis not being tuned properly.

You mean the following error increasing? It always stays below one encoder count. I think the stairsteps you see are an artifact of some kind of interpolation based on velocity and interval. One encoder count amounts to 8┬Ám.

I'm pretty sure the tuning can't be much improved at this (low) speed (without changing to a higher res encoder).
Last edit: 22 Apr 2020 12:30 by rmu.

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22 Apr 2020 14:59 - 22 Apr 2020 15:00 #165113 by PCW
Replied by PCW on topic Following Error When Homing
Hmm something is different but I'm not sure of the cause.

In your plots, the encoder position reset happens one
sample later than the index-enable falling edge
In my simple test, the encoder position reset happens in the
same sample:

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Last edit: 22 Apr 2020 15:00 by PCW.

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22 Apr 2020 15:16 #165118 by rmu
Replied by rmu on topic Following Error When Homing
Maybe that has to do with pid.x.error-previous-target true. I will try again setting this to false.

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22 Apr 2020 15:34 #165122 by PCW
Replied by PCW on topic Following Error When Homing
Well it _should_ not (index-enable should be an input only to the PID component)

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