Z actuator o-ring failure during slide scan

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Hi all,
I recently built the latest v7 beta version and installed Server v3.0.0-alpha 4. First I just want to say that it really is incredible to see how far this project has come. Amazing job to all those involved, the build process, calibration and scanning is so impressive. I cannot imagine the amount of work involved. Huge thanks to you all!

I have been running a lot of slide scans (it’s addictive!) and recently just as the scan finished and the microscope started moving home I heard a snap. I played around moving the joints and all seemed ok. Then I put in a new slide and was unable to focus. I finally realised the snap must have been Z which I wasn’t expecting since its motion is so small and all my failures in the past have been X or Y.

Happily only the o-ring had failed, so I just replaced it and went right back to scanning. But now I’m wondering about the Z range in these automatic scans where over a large sample it may exceed some Z limit trying to stay in focus. Especially since we can see the X/Y positions printed in the log but not Z. Does this matter? Was my failure unusual?

It also got me thinking about where I should start with the optics. Seems to me if I deliberately install the optics too low initially with the m3 bolt then I will need to electrically move Z up to get in focus which reduces starting tension on the o-ring. Again, does this matter? Am I overthinking this and I just had an unlucky failure?

Thanks, Al

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Glad you are enjoying scanning.

O-ring failures are really hard to diagnose. They generally happen infrequently and we have not been able to discern an actual cause. There is an issue thread on GitLab Identify reasons for Viton bands / O-rings breaking (#462) · Issues · OpenFlexure / openflexure-microscope · GitLab which is mainly about breakages during assembly, but many of the questions also apply to breakages in use.

In your case I would expect that it has no particular cause. Was this a recently assembled microscope? The actual range of the actuator column on z is smaller than the x-y actuators, so even at full stretch (lowest position of the lens) it is only up by a little.

It would be interesting if you could post here if it fails again

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Thanks William.

Yes the breakage was on the same day as the build. I will report back if it happens again (or doesn’t).

Regarding installing the O-rings, is the “nut tool” supposed to block the actuator moving up as we push the band tool up. So it should be pressed up in contact with the screw under the nut (red box in below image) not on the actual nut is that correct?

nut tool
nut tool389×481 12.4 KB

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Yes, ideally it goes in under the nut. As long as it is into the central column that will lock it enough, sometimes there is not space under the nut.

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