Steppers & Linear encoders

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12 May 2009 11:56 #243 by gtom
Replied by gtom on topic Re:Steppers & Linear encoders
Well, i think that a component between axis* and stepgen* ist the best solution to integrate the linear-encoder.
Another advantage is that emc can stop on lost steps also cause the stepgen* and axis* are not modified. We'll be still able to use position feedback and fmin_error / fmax_error the same way if've already on my machine. Need some test now to see if such a component makes sense or not...

regards, Thomas

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12 May 2009 12:11 #244 by BigJohnT
I'm not sure if you know about CVS but you can download a CVS checkout and configure a run in place. This is an easy way to test your comp out each time you modify it.

http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Installing_EMC2#Getting_the_source_with_CVS
http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?CVS

http://www.linuxcnc.org/docview/html//hal_comp.html

Regards,
John

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26 Jul 2020 19:54 #175958 by Joco
Replied by Joco on topic Re:Steppers & Linear encoders
I realise this thread is old but it is "on topic" to what I am starting to look into and didn't want to raise the same topic again if there was undocumented success here.

Thomas - did you ever solve this? I see 2.8 has external oiffsets that could be the answer under latest available capabilities.

Anyone else - if there is a better/newer thread on this use case please just post the link and I'll hop across.

Cheers,
James.

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26 Jul 2020 20:48 - 26 Jul 2020 22:14 #175968 by tommylight
There are other threads that discus using steppers with encoders, so if the scales are incremental ones, the same applies.
And thanks to tireless work of Chris and Co. the pncconf wizard now makes 99% working configs for such systems using Mesa boards, the only thing left is to omit the feedback fro the stepgen and set it to encoder, all in all about 3 to 5 minutes of file editing.
Last edit: 26 Jul 2020 22:14 by tommylight. Reason: typo

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26 Jul 2020 22:12 #175986 by PCW
Replied by PCW on topic Re:Steppers & Linear encoders
"MetalMusing" has quite a few YouTube videos plus a thread here that I cannot
find ATM...

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27 Jul 2020 11:44 #176068 by rodw
Replied by rodw on topic Steppers & Linear encoders
Any discussion around steppers and encoders should now include smarter drivers like the LAM DS series that have a boost function that allows the current to be increased to the driver as required. Tommy has experimented with enabling this boost feature based on following errors measured via an encoder. However, a more normal use would be to reduce the current when the axis is coasting at speed and not accelerating (which is where the greatest torque requirement occurs). From the modelling we've done, a well matched stepper motor may require a lot lower current than its maximum rating to do a particular job so it all starts to make sense.... So if additional current was boosted when the following error got close to loosing steps, the drive might be able to catch up.

I will be experimenting with this when I get to it. I was thinking of building a component that reduced the current if the velocity was not changing between servo periods. If you have a system designed to work at up to 10 m/min and its only moving at 2m/min, it stands to reason the torque requirements are much reduced so there is a lot of scope to be gentler on the drives.

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27 Jul 2020 15:04 #176081 by tommylight
Rod, are you gona be using encoders?

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27 Jul 2020 16:57 #176098 by Aciera
Replied by Aciera on topic Steppers & Linear encoders
I use steppers in closed loop with glass scales on my mill with a 7i76E. Works fine.

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27 Jul 2020 19:24 #176131 by rodw
Replied by rodw on topic Steppers & Linear encoders

tommylight wrote: Rod, are you gona be using encoders?


No I won't. I did buy one to experiment with but good encoders are awfully expensive. I thought a better approach was to enable boost only during acceleration/deceleration via a separate component. In a lot of instances, this would be for only a very short period most of the time so the drive could idle once at cruising velocity . That seemed to be more the way Lam suggested how to use the feature.

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27 Jul 2020 19:34 #176134 by tommylight
OK, waiting patiently for the results.
The following user(s) said Thank You: rodw

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