On Sunday, September 6, 2015 at 09:28, Ryan Carlyle wrote:
The big issue with most high-ratio extension mechanisms like scissor lifts, aside from cumulative slop/backlash at rotary joints, is that there's a non-linear relationship between actuator motion and stage motion. So you need to get the kinematics into firmware, and resolution isn't constant. So some cleverness is required...
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WW, you ever thing about taking that super telescoping jig (portable scanner?) and building a Z stage like that? I'm guessing the precision isn't high enough, but I'm sure it crossed your mind?
On Sunday, September 6, 2015 at 17:30, Ryan Carlyle wrote:
I love the "print your own Z stage" approach. Awesome concept. Lots of engineering challenges with that though.WW, you ever thing about taking that super telescoping jig (portable scanner?) and building a Z stage like that? I'm guessing the precision isn't high enough, but I'm sure it crossed your mind?
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use as many wobbly joints as possible
- The X bridge pivots to keep the extruder vertical as the XZ tower rotates up
- The Z mechanism lifts the X bridge straight up as the XZ tower rotates up
- The Z actuator linkage is linearized, so you don't need special firmware and the Z resolution is constant
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On Sunday, September 6, 2015 at 23:09, Ryan Carlyle wrote:
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Ah, I hadn't thought of that. Wow, that's a lot of linear rails...
Speaking of a pantograph, you could make the horizontal arms half the length of the vertical ones so that they would only travel half way across. This would allow you to bring both sets of horizontal linkages into the same plane, cutting the height of the mechanism and also letting to get rid of one of the linear rails (instead using two carriages on the same rail). You'd halve the resolution of the Z axis, but I'd want to use a geared motor there anyway (I've never liked the resolution of belt-driven Z).
OTOH, you could make that a screw-driven axis, but you'd lose the easy ability to drive both directions at once unless you had a custom screw made that was half left-handed (actually, with a large enough lead/diameter ratio, I bet it would be possible to make a dual thread screw that would work with both left- and right-handed nuts along its entire length... that would be crazy!)
Don't forget the parallelograms, or did you have a different plan for handling that?
I don't think you need to worry too much about a low-profile hot end. Just design it so that the platform has to move forward for the Z to fold all the way down, and the hot end can dip below it for transport. Even if you switch everything (including the bottom frame) to 1515, you'll have more than 60mm of height fully folded once the parallelograms are added, and an e3d v6 is 62.3mm long. If you have a bowden coupler at the very top of that that you disconnect for transport, you shouldn't have any trouble stashing the hot end inside when it folds up. If you keep the 2040 for the bottom frame, that should give you more than enough space for a direct-drive extruder with a MK7-style hot end if you arrange the X axis carefully.
Simplify it. Use only one of the linearizing pantograph mechanisms and use a passive cable drive to keep the two horizontal carriages in sync.
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I wasn't thinking about using a cross-beam. It looks like the tension on the cable would make the beam want to skew. If you designed it to be skewed the other way a few degrees, the tension would push the wheels against the frame sides, and you may even be able to make it work without the outer wheels. You could also just balance the forces by adding a second cable as a mirror image of the first. Because the relative Y-axis positions of the two pulleys is constant and the pulley rotation direction is the same, you could do this by running both cables around the same pulleys (crossing around each pulley, and again in the middle) so that you don't need more pulleys to add the second (mirror image) cable.What I was thinking of was a cable in a figure-8 loop, so that the two sides would move together and the forces would be balanced. In that case, the cross beam shouldn't be necessary (though it would make the initial syncing of the two sides easier, and aside from adding inertia, it shouldn't hurt anything). This would require four idler pulleys, while as I mentioned, you could do your version plus its mirror image with only two.On Monday, September 7, 2015 at 14:33, Ryan Carlyle wrote:
Here's the simplified, low-profile version with some of WW's suggestions:--
I'm not at all committed to the MGN12 and belt drive for the Z actuator. A belt + V-wheels would avoid grease mess, but a linear rail and screw would probably be more precise. (I'm not a huge fan of V wheels on 2020, and it's arguable whether adding envelope for 2040 is worthwhile here.) Lots of options. Just needs very high bending stiffness (no 8mm round rods).
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I wonder how many cycles it can do before the metal starts to fatigue.
I wonder how many cycles it can do before the metal starts to fatigue.
Current plan:
- 4-5" cube working volume
- 300x250mm footprint to fit in a backpack (a little bigger than a textbook)
- Trying for <100mm thickness collapsed, doubt I'll pull it off though. 125-150mm would probably be fine.
- Structural frame a mix of 2020 series extrusions (eg probably some 20x80 in there)
- All moving linkages will be 1515, connected with printed parts and probably 623 bearings
- One side of the Z lift will have a full pantograph with the other side most likely cable-sync'd per WW's suggestions
- MGN9 rails for Z, Misumi PLRH for Y bed, not sure about X yet -- thinking mini V wheels or another MGN9 or even a couple 8mm rods just because I have them on hand
- Short-throw Bowden, probably a B'Struder
- Unheated build plate
I'm not too far into it yet, mostly just working on general mechanism layout right now. Fitting all the parts into this kind of envelope is hard.
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Here's another neat "collapsing linear actuator" concept I just found. Basically you push anti-backbend chain out of a storage cartridge. Combined with a linear rail or another chain oriented the opposite direction, it gets you a linear stage. I doubt it's precise enough for standard 3d printing, but it's a possible candidate for the "self-printing Z-stage" type actuator. The printer could literally construct more chain links as it extends.