RepRap: Blog

Minimal updates for a week or two as I'm preparing for and heading to EverythingOpen in Gladstone, Australia to present on the Quirkey accessibility keyboard. This takes me away from the hardware which is a bit of an embuggerance in the development department. I'm deliberately not fixing a broken axis at the moment so I concentrate on the presentation, trip prep., instructions for house-sitter, last minute house maintenance etc.

There is some new software I'm working on though, to create test gcode patterns. I have that and new stage designs to work on while stuck in airports and hotels, so expect to be fully occupied.

# posted by vik-olliver @ 9:33 AM 0 comments

Just posted this on the wiki, and posting here for comment:

"As with the original RepRap, it is hoped that once the first μRepRap is operational, it will be able to replicate. Unlike the original, the replicant will not be identical to its parent but will be a much smaller functional equivalent. Control of the replicant will be difficult, but not impractical. Options include perpendicular magnetic fields, inducing vibrations to operate ratchet mechanisms or tuned structures, or at its most basic cranking the mechanism with the tip of a probe until something better can be worked out.

It might also be possible to fabricate a μRepRap that is scaled down further. Assume that a RepRap has a precision of approximately 0.2mm on a 200x200mm work area, and a μRepRap has approximately 1 micron resolution on a 10x10mm work area. We see roughly two to three magnitudes in reduction in scale. If flexure systems also scale, then it might be possible to use a μRepRap to create a smaller printer with a resolution on the nanometre scale. Unlike current attempts to operate with nanometre precision with macro scale hardware, errors in the device due to thermal expansion and other material-related noise would be much reduced. It would at least be interesting to see how far this limit could be pushed."

# posted by vik-olliver @ 7:13 AM 0 comments

I keep snapping the 'O'-rings on the OpenFlexure stage, probably because I'm pushing the range of movement more than the average microscope user. That's going to have to change, probably using anti-backlash nuts like the old Darwin printer's Z stage. There are a few other things I want to hack about: Proper motor mounts, extra platforms and attachment points, new flexures, better gearing, more access the the mechanism, cable guides etc. but it's going to have to wait until I've finished presenting at EverythingOpen. Once I've decompressed from that trip I'll be able to focus on μRepRap properly. I have some photosensitive resin ready for dip-pen tests too, but blowed if I can find my stash of UV LEDs anywhere.

I plan on having a darkened resin reservoir on the slide, and illuminating from below. This will avoid having to shield the probe or the resin reservoir during UV exposure cycles. Hopefully cheap soda lime glass slides will let enough UV through.

# posted by vik-olliver @ 9:35 AM 0 comments

I should probably have mentioned this earlier, but in order to run the stage it helps a lot to have some way of levelling it. So I modified the OpenFlexure Delta Stage feet (STL files here) to accept microswitches, which can be wired up as the negative endstops for the GRBL CNC driver. This is never going to level the thing to the nearest micron, but it gives you a convenient way of getting to some kind of starting point. Once you have levelled it, you can just return the axes to zero before powering the stage off. I'll add a home button to the Control Panel later.

# posted by vik-olliver @ 9:21 AM 0 comments

I've separated the GRBL/delta Control Panel code out into three modules to make it easier to maintain. They're not "proper" python modules yet, but it all works https://github.com/VikOlliver/RepRapMicron. Now it actually has a V0.01 version number!

[Updated update: Now modules are used properly]

# posted by vik-olliver @ 4:38 AM 0 comments

I've tried to make the software I'm using to control the prototype available on Gitlab, but I don't seem to be able to set it to public. So, back to GitHub it is: https://github.com/VikOlliver/RepRapMicron

As a quick update, here's progress. We're down to a 0.2mm square etch now:

# posted by vik-olliver @ 10:27 PM 0 comments

Cut to the chase, first output proving the delta mechanism and code. A 0.5mm square drawn inside a 1mm square:

In the lower right corner you can see an M3 screw thread (and its shadow). This has a pitch of 0.5mm, so I used it for scale (which is undoubtedly not perfect yet, but close). I'm sure I can do a lot finer, but this is the first ever test and I'm using a relatively huge needle point that I can actually see with modest magnification. Sorry about the lighting, fix that in the next version.

The hardware is a modified OpenFlexure Delta Stage with the multipath lighting platform on it, which I have uploaded here. Attached to that stage is a probe arm, 3D models found here. The probe arm mechanism allows coarse manual positioning.

The feet of the modified stage contain microswitches (files found with the probe arm), which allows the GRBL firmware on the RAMPS board to roughly level and position the stage using the standard homing algorithm. I'll upload the configuration later, but it is using Robotini GRBL Servo code with the Configuration.h file modified to allow simultaneous homing of X, Y & Z axes.

The PC-side probe control software is ugly work, but I am working up the courage to post it. Have patience. Update: I put the code up.

# posted by vik-olliver @ 3:17 AM 1 comments

Following input from the OpenFlexure folk (hi Richard!) I found their code uses approximations, which line up with my IK model ... except where I forgot to rotate an axis properly. Yah. My 2-point 3D rotation maths is busted for unclear reasons, but once that's fixed we should have much more reliable positioning.

Also the OpenFlexure team might be lending some part-time support, which will be most welcome.

# posted by vik-olliver @ 10:21 PM 0 comments