Retrofitting Mikron WF41C: Distance coded homing success

PS: ...the only way I could find so far to have an encoder reset during a move without the jerky stuff was by driving the servo directly with a constant voltage during homing. But I doubt that this is the way to go....

This suggest that the index_enable falling edge -->PID suspend FF1 calculation scheme is not working for some
reason. This normally works fine for velocity mode servos so your disable reset on index workaround is not required.
I have heard of this symptom occasionally but have not determined the exact cause.

That said, I think a better overall index system is to always latch the position on index and have LinuxCNC
use the latched position for its internal offsets and avoid steps in the joint position. This also has the advantage
of being able to use index for a position sanity check. The disadvantage of this method of index handling is
that some encoder counter hardware may only have the option to clear the count on index.

Hi Marc,
Please inform me about the servo motor , encoder , and drives part or model numbers and its specifications if possible.
Best regards,
Heggy

Hello,

another update from our retrofit project...

Y-axis ballscrew issue: I happened to find on ebay the exact ballscrew assembly for my machine in good condition at a price slightly below what I would have paid for the axial bearings only. So we bought that assembly and now have the machine back together.

Distance coded homing: After having the machine back operational we could continue to test distance coded homing and we know can reliably home the machine on all 3 axis! Basically it is just working now without any fuss at all
Currently the modifications I have done to the linuxcnc code are in the hm2 (extended to detect the index-position without resetting) and in the homing procedure itself where an option for distance coded homing was added. Besides a little bug we had to fix the code corresponds to what I posted in 209052 . The exact code can be found in my branch on GitHUB .
It actually took as a while to get it running on the Y-axis which proofed to be unrelated to the code. The problem simply was a cheap d-sub 9 female connector which sometimes didn't transmit the glasscale signal reliably.
Lesson learned: the glasscale signals are definitively delicate and all the shielding an high-quality connectors that come with the Heidenhain originals are there for a reason...
But in the process of debugging this issue the modification to hm2 became very handy as we could use it to check consistency and found that counts were lost sometimes between index-marks. So along the line what @PCW wrote in an earlier post I will keep the modification in the hm2 and implement an additional component for sanity check of the encoder signal.

PID tuning: After the initial quick success we had with the PID tuning process we realized that we are not done yet. While we really could bring the f-error down below 0.002mm with just tuning P, FF1 and FF2 as well as the current offset we found now that just adding some weight in the form of e.g. a vise is affecting our setup significantly. So some more work on PID tuning is need to give that machine a good performance over a wider operating envelop (actually I think the machine is specified for table loads up to 400kg).
I'm currently thinking about writing an optimization procedure in an external python script that would execute the same G-code reference program over and over again, accumulating the integral of the f-error as well as the max and then use some probably gradient based optimization algorithms from scipy to optimize the setup. Could this make sense? Did already someone do something like this?

Best regards,

Marc

Hi Marc,
As you were thinking about writing python script that would execute g code....etc,
This repository contains a collection of Python scrips that generate simple G-Code for LinuxCNC.
github.com/LinuxCNC/simple-gcode-generators
All of these scripts, written by various authors, are licencing under the GNU General Public License.
You can either clone this repository using Git or download the whole repository as a zip file.

There are another links which i think that it will be useful to read before you begin:

linuxcnc.org/docs/2.6/html/remap/structu...:unallocated-g-codes
Python / GUI / QTpyVCP / GLADE
linuxcnc.org/docs/2.6/html/common/python-interface.html
qtpyvcp.kcjengr.com/
linuxcnc.org/docs/html/gui/gladevcp.html
Install GLADE 3.8 on debian 9 forum.linuxcnc.org/9-installing-linuxcnc...lade-linuxcnc#112162


Best regards,


Heggy

Hello Andy,

sure I would be interested in testing.

Here in Europe you can find (typically Heidenhain) glasscales used starting at around 200Euro on e-bay. They are named something like LSXXXC (mine are LS403C). Important is the C at the end because only these have an index track for distance coded homing.
If you find one we would be happy to contribute one of our little interpolation boards for testing.

Best regards,

Marc

@cscegypt
Thanks!

HI Mark,
Good Day,
I just imported the same WF41C Mikron Machine from Europe. . I would like to use similar modified controller after you finish from designing.
Please inform me about the nice possibility of transferring similar system which you are doing / estimated cost and time /Quote.
Best regards.
Heggy