Compliant Fractal Gripper

thingiverse

A compliant mechanism take on the Fractal Vise, inspired by [TeachingTech's more traditional model.](https://www.thingiverse.com/thing:4904044) After printing, be sure to go through and detach the pivot arms from each other. They're printed 0.4mm apart, but they still tend to stick together, since the flexible filament droops a lot when bridging. It'll sort of work if you don't break them apart, but the compliance improves a LOT once they're separated. The underlying concept is very much the same: each pivot tends to (nearly) balance the torques on it, so all the tips tend to try to equalize the pressure on them, or hit a limit trying. In the traditional design the limit is a mechanism that prevents the subassemblies from rotating further; in the compliant design, the subassemblies just bump against the parent assemblies. The arched design is intended to maximize the room available for the subassemblies to rotate, but you can see in the photos that the limits do still come into play. Another limitation on this design is that the pivots here aren't neutral--they have a certain amount of centering spring force. The same springiness is also what prevents them from collapsing and allows them to transmit the clamping pressure, so finding the right size for these elements is something of a balancing act: too strong and the jaws will fling away what you're trying to grab, but too weak and you get very little gripping force at all. I've mostly erred on the side of the latter here; these will conform easily to the shape of the thing you try to grab, but they don't support a very high actual grabbing force. So they're not much use as an actual vise. I'm thinking they might be useful as a gripper for a robot arm, or maybe even as a foot for uneven terrain. I haven't quite got the pivots and springs perfectly balanced--the smallest jaws don't tend to move much, because the contact points on them are so much closer to the pivot, and I had to make the pivots a minimum size in order for PrusaSlicer to print them at all. So they're of limited actual use in their current form. But I wanted to share them, because I think they're such an entertaining demonstration of the concepts involved.