Roller Milling
Spent some time working this out on the whiteboard today, and threw together some rhino sketches.
I'm going for simple, strong-enough, and easy to build. Using rollers and pulleys, or, just as easily, rack and pinion or leadscrew-type actuation.
Next up, getting into fusion to get through the details, then fabbing one axis... designing a simple 3axis machine, and fabbing that.
I pulled this off with a simple set of flat-milled parts - I was trying to work with the constraints present in the set of FREP and Milling tools in MODS, to see if we could finish end-to-end gantry generation and milling.
The result is OK, it'll certainly do - there's a line to toe between being kinematically wicked and loosing complexity. This is a bit of a midpoint - all of the axis of constraint have 'tuneability' in that their preloads can be adjusted, but all are over-constrained. There's enough (lots) flex in HDPE that this will be OK. There's a version which (not actually existing yet) is dead simple and totally constrained, and a version which is perfect motion-wise.
Overall, it's a bit bulky. There's some detailing left out before it is complete. But I think in terms of an all-arounder axis, this is pretty OK, and certainly OK for being millable from one sheet of HDPE (or alu, whatever).
CAD
Available Here: https://a360.co/2qQf6wf
password is rollercoaster
The gantry is built with a set of 'kinematic elements' - a Motor / Pulley Unit, Lateral (into the gantry) and Cross (across the gantry) supports:
These can be jimmied around to make a full set of constraints:
And combined into a complete gantry:
Here's the back of that:
Hardware Notes
- needs more clearance on belt-side
- belt tensioning?
- when rounding corner, teeth must at some point disengage b/c different lengths
- same size M3 tensioning
Motor Idlers / Topside Way Bearings mount on M5 SHCS with washers on both sides and washers used as bearing shims. Use 3DP bushing (or purchased?) in axel. Important for carrying some moment to plate.
Clearances here for pulley to be mounted / tensioned! Consider order of assembly, tensioning.
M5 Nuts 93625A200 M5 SHCS (length not selected) 91292A128 M5 Washers 93475A240
also uses long M3's for tuning, nuts, washers. Length to be selected.
Some Simulation
It occured to me in class today (Rob Hart fabricated the below component!) that the two-bar flexure I had intended was acting much more like a one-link flexure. Whoops, all well. Still does its job. Here's an image of that in any case: