RepRap: Blog

The new X & Y stages are moving smoothly enough in 10μm steps. Remember this isn't corrected for arc movement on the flexures, but what it does it is pretty repeatable. I've tested it at ranges of +/-4mm against a 0.1mm grid, and in the photos below against a 0.01mm per fine division grid. Sorry about image quality, but my homebrew test system involves sticking bits of painter's tape on the screen viewing the USB microscope. Painter's tape does not screenshot well. Here's my view at (0,0) and offset by 0.2mm & 0.3mm on both axes simultaneously:

So from this I'm getting 15-ish microns from where I'd expect to be, but like I say this is repeatable rather than linearly accurate. Not getting any indications of backlash above a micron either (a guestimate based on sub-pixel flicker, which is bloody obvious on low refresh rate cheap USB miscroscopes). So if I can map out a grid and apply corrections, and they turn out to be consistent with long term use, then near enough to micron accuracy looks achievable.

This is good. It gives some validation to the performance of the XY table and the long flexure rods used to drive it. With motion ranges of a few mm the X axis position doesn't seem to be affected visibly by the Y axis within margin of error of my microscope. Here's a picture of the current setup:

The connections between the drive stage and the flexure rods are a bit rough. The new driver stages are a different size, in a different location, at a different level, and I haven't had the chance to fix it all up properly. It was thrown together from what was at hand and needs all-round improvement - though didn't wobble at all during testing.

Next up, I'll get working on a Z axis. When I know where that needs to be I'll improve the bracing and fixture locations all round. Then we need a probe and end stops, and we'll be in the same position as we were when the OpenFlexure stage died.

Except this time I can put it all on github under the GPL. This needs to be done in time for Everything Open 2025 on the 25th January, because guess who is doing the first presentation of the conference in Room A after the keynote: https://2025.everythingopen.au/schedule/

# posted by vik-olliver @ 5:20 AM 0 comments

I made two black PLA driver stages and they worked fine. I made a white one and it didn't. Hmm, time for science. I made two 100mm beams with a flexure and anchor on one end, and put 20g (OK, two 158 grain .357 lead projectiles, which is close) on the end of each.

Camera lens positioning is tricky here, but the anchors are 38mm above the desk. The black PLA drops to 22mm, and the white PLA only drops to 28mm. My maths is generally suspect, but this indicates to me that the white PLA is significantly stiffer (10mm deflection vs 16mm deflection) and that this is affecting the performance of the flexures in the stage.

For reference, the PLA is the stuff I used to make as Diamond Age using Ingeo 3251D PLA (a relatively low molecular weight). The white is '3DEA Paper White' and I have no idea what they use but I suspect (a) most manufacturers are using higher molecular weights these days, and (b) it is packed with a lot of whitener which will affect the stiffness anyway.

So from here, I make another in black and see if it works, then produce modified flexure designs to match the flexibility with the white and test a stage using those flexures. [Edit: A third black PLA drive stage works fine.]

It may be that I need to include a stiffness test article for people to use to optimise their μRepRaps.

# posted by vik-olliver @ 6:52 AM 0 comments

I've been quite busy in the background. I've been through about 5 iterations of the stage, finding out there to reinforce, lengthening arms, changing mount points, testing various drive nuts, changing flexure profiles etc. I've eliminated the vertical flexure in the arm as the drive nut translating left/right has an unexpectedly large impact on stage movement. I've also had to shorten the flexures to 2.5mm reduce twisting. Here's a part of the prototyping debris:

I was getting some curious flex at one point, which counteracted the movement of to top of the stage, making the movement appear uneven. This is because I was supporting too close to the motor, which it turns out needs to free-float. This has lead to a change in mounting. I've increased the mechanical advantage to 3:1, and the range of accurate motion should still be in the +/-2mm area with inaccurate motion possible +/-4mm without breaking anything.

As you can see on the yellow stage at the front, I've the beginnings of a new probe arm coming together which is much lower profile, allowing the USB microscope to get much closer and thus provide better resolution.

The M3 Nylok nuts appear to wear out after a few assembly/disassembly cycles, so I'm back to locknuts on the drive screw. The drive nuts are back to ordinary M3 nuts again rather than sections of brass pillar, which had just too much slack in them. The modules are slowly getting easier to assemble/disassemble, and there are a few spare mount points that can be trimmed off now I know where things are headed.

With the new arm/pivot lengths and new mount points the drive stages don't match the XY table quite so well, so more tinkering required there. The blue Z stage drive won't fit the new probe holder, so that has to change. I'm planning on using the same stage driver for all axes to keep things simple. From the development viewpoint anyway.

The black is a much more optically sound colour, but it is much more difficult to determine what is going on. Unfortunately, I have a lot of black PLA, and the bright colours are being nicked by the family for Xmas decorations, so black it is.

Season's Greetings all.

# posted by vik-olliver @ 10:55 PM 0 comments