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Flexure that allows for Configurable Positions

JollsJolls Member Posts: 77 ✭✭
edited August 2 in Using Onshape
I have a parallelogram flexure and for visualization purposes I'd like to have the assembly with a couple different configurations showing the flexure with different bends. How have you guys done this in the past? The only "bend" I really know of is sheet metal and while that might work I thought I'd ask here before I put in the work to make a flexure into "sheet metal" (even though it's not sheet metal) just for visualization purposes.

A simple example would be a cantilever with fixed position on one side and a variable force on the other side. It'd be nice to bend the cantilever showcasing various bent positions.

Comments

  • S1monS1mon Member Posts: 887 PRO
    There are some FeatureScripts which try to simulate flexures, but nothing super accurate that I've seen yet.

    I would model the legs of the parallelogram in a way that you can easily vary a dimension to drive the different positions, and I would loft the flexure portions between the legs. You'll have to be somewhat clever about controlling the length of the neutral axis in your layout sketch (if you're going for accuracy).
  • JollsJolls Member Posts: 77 ✭✭
    S1mon said:
    There are some FeatureScripts which try to simulate flexures, but nothing super accurate that I've seen yet.

    I would model the legs of the parallelogram in a way that you can easily vary a dimension to drive the different positions, and I would loft the flexure portions between the legs. You'll have to be somewhat clever about controlling the length of the neutral axis in your layout sketch (if you're going for accuracy).

    Thanks. I was considering doing something like that too. It's just drastically more complicated than a simple single sketch extrude which is how this flexure is designed now. But I may just have to do it. I also just considered making an assembly and effectively cut it into 3 parts (fixed, flexure, moving part) so I could at least better illustrate how the device works. Clunky but easy. And not as clunky as just having a static flexure.
  • eric_pestyeric_pesty Member Posts: 338 PRO
    You might be able to do this by keeping the different "sections" of your flexure as separate parts with small gaps between them until the bottom of the tree and then do a few "transform" commands to align them before connecting the bits.
    You could also create separate bodies for the straight and bent positions of the "legs" and then configure the selection of a boolean to create the different positions (and still use a transform to move the part that doesn't deform).

    A 2D skeleton sketch showing the start and end positions would really help here as well though...
  • Evan_ReeseEvan_Reese Member Posts: 1,424 PRO
    You can dimension the length of sketch arcs and sketch splines, which could be a good approximation. For arcs, dimension the end points, then the arc itself. For splines just click the spline. Here's me just dragging the sketch, but you can see how it could be configured. Is that what you're after?

    Evan Reese / Principal and Industrial Designer with Ovyl
    Website: ovyl.io
  • eric_pestyeric_pesty Member Posts: 338 PRO
    You can dimension the length of sketch arcs and sketch splines, which could be a good approximation. For arcs, dimension the end points, then the arc itself. For splines just click the spline. Here's me just dragging the sketch, but you can see how it could be configured. Is that what you're after?
    Ha, I didn't even know you could dimension the length of a spline! I'll have to remember this!
  • Evan_ReeseEvan_Reese Member Posts: 1,424 PRO
    yep! It's handy just rarely enough to forget it's there in between uses  :D. I look forward to a proper path length dimension that can be applied to whole chains of curves.
    Evan Reese / Principal and Industrial Designer with Ovyl
    Website: ovyl.io
  • JollsJolls Member Posts: 77 ✭✭
    You can dimension the length of sketch arcs and sketch splines, which could be a good approximation. For arcs, dimension the end points, then the arc itself. For splines just click the spline. Here's me just dragging the sketch, but you can see how it could be configured. Is that what you're after?


    I think that could work in some of the single-axis flexures for sure! I did a flexure like this over a year ago and didn't configure it like this but probably could have and gotten some good results. My current flexure is 2D so I'm not sure how a sketch would work. What I ended up doing was splitting the base from the other side of the flexure and just configured the offset. The flexure looks broken that way but at least the parts are positioned in the right location.
  • Evan_ReeseEvan_Reese Member Posts: 1,424 PRO
    Do you mean your current one is 3D? It's hard to weigh in much better without info on what exactly you're trying for.
    Evan Reese / Principal and Industrial Designer with Ovyl
    Website: ovyl.io
  • JollsJolls Member Posts: 77 ✭✭
    Sorry, here' s a picture. Worth a thousand words. This is a mockup of a disposable tray that holds a sample in the middle. The outer portion stays fixed while the center square (with the big hole) moves down ~10mm The flexure will "scissor" open. What I did on the 2nd picture was "snip" the flexure as a configurable checkbox (unsuppresses the remove-extrude) and created an assembly that allows me to configure the offset between the two parts.

    I guess, if I used your spline example I could extrude it from the side (so the spline would be a sideways V) and then come in after that extrude and cut in the flexure shape. Maybe that would work. MIght have to give it a go now that I'm thinking about it.



  • eric_pestyeric_pesty Member Posts: 338 PRO
    You should be able to fake this fairly convincingly with a few features as it looks like it should only deform in 2D.
    I completely remove the flexing bits and do a transform of the middle section to move it to its deflected position and then try to model the "ramps" in the deformed position but in such a way that would still work with zero deflection (if that makes any sense).
  • JollsJolls Member Posts: 77 ✭✭
    Alright, I was able to put in a master sketch and build the flexure from that. Now it's highly customizable with a few variables. Gap, flexure thickness and width. Along with the "flexed" offset. This should let me get the concept across better. Thanks for the assistance!


  • Evan_ReeseEvan_Reese Member Posts: 1,424 PRO
    ooh fancy! It seems like a good enough approximation. It doesn't simulate any of the torsion you'd actually see, but definitely close enough to illustrate it.
    Evan Reese / Principal and Industrial Designer with Ovyl
    Website: ovyl.io
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