Design concept: flexure + stepper

[NemoAndrea]

The Medjed system needs a fairly high accuracy (<1um step) and high rigidity Z-focus mechanism. One explored design relies on a standard linear rail for the motion guidance and stability, but I was curious to see if the same could be achieved with a flexure within the project budget.

Why? Linear rails are very nice, but they are a bit annoying to work with, requiring correct grease application. A functional flexure would be easier on maintenance and is well suited to an application with small displacements such as an objective fine focus.

My initial idea was to run with a common double-leafspring arrangement 📑, which theoretically has no parasitic movement and does not require any FEM calculations to ensure proper behaviour.

My initial idea was to run a symmetric design (i.e. two double-leafsprings):

The symmetry will at least help with ensuring the objective remains parallel to the optical axis, but it does make the assembly a bit bulky, which is not a fatal flaw, but warrants exploration of other geometries.

🤔 What about materials?

Flexures are traditionally machined out of metals. This is because metals have very low creep, whereas plastics always have some creep (going for glass/carbon fiber filled plastics can help a bit). In addition, metals can be cut to shape with 🧵 wire EDM, which allows for extremely tight tolerances and high performance flexures.

Now, I am pretty sure wire EDM is not within the project budget (remember: parts must be sourceable), so there are two alternatives:

1. 3D printed SLS/MJF parts (glass filled ideally)
2. Waterjet cut parts

The latter would be better for flexures, but would likely significantly increase costs as the waterjet part would still need some extra machining done on it to be able to mount additional (3D printed) brackets onto it.

Anway, an interesting area to explore...