RepRap: Blog

Had a thought while trying vainly to sleep last night. I've tried using a parallelogram flexure before to make a pantograph, which in theory works but in practice is not sufficiently stable. I realised that if I made essentially an asymmetric pantograph I could at least achieve stable and constrained motion in one axis:

There's probably a proper technical term for this arrangement but I don't know it. When moving the free end (yellow) towards the (blue) pivot, which would be done with a drive screw, the joint indicated by the green arrow also moves linearly towards the pivot over a reduced distance. This mechanism would be relatively easy to constrain and hold firmly.

The result would be a linear actuator that didn't pivot, unlike the current design which basically relies on a rotating lever which effectively gets shorter towards the limits of its range of motion.

Assuming I can get a 10 degree total movement out of the flexures, and want to have an 8mm range of motion with the same 3:1 reduction ratio, my vague maths suggests the shortest linkage needs to be about 23mm long. That would make the long beam 92mm long, which is a bit longer than the current beam but not outrageous. I suspect the flexures would survive more than this but might not be linear at the extremes, so the beam could be shorter.

Thought: Might have to extend the drive screw to 60mm.

I don't intend to pursue this immediately, so feel free to have a go at it yourselves. I still have much to learn from the existing mechanism, which while not perfect is quite good enough for this stage of the project.