Sasini Wickramatunga

Chapter III

A Desk-Sized Flexure Stage

Sub-micron motion with no bearings at all

In progressJun 2024 – ongoing

Blueprint-style drawing of a rectangular stage held by four thin leaf springs.
Plate IIIRevision C of the stage, drawn as a blueprint.

Ball bearings rattle. Sliding rails stick. A flexure doesn’t have either problem, because nothing in it slides: the whole mechanism is one piece of material that bends a little, the same way every time.

I wanted to know how good a flexure stage could be if it came off a hobby 3D printer.

Design

Four thin leaf springs hold a central platform. Push the platform and the springs bend in an S-shape, so the platform moves sideways while staying parallel to itself. It’s the same principle as a parallelogram linkage, without any pins.

Beam theory predicts the stiffness of each leaf as k=12EI/L3k = 12EI/L^3, so the stage should be very linear for small motions.

Measuring it

Using a dial indicator and a set of calibration weights hanging over a pulley, I pushed the stage in 0.16 N steps.

Displacement versus force plot showing measured points close to a straight line
Measured displacement versus applied force. The stage is about 4% softer than beam theory at the top of the range.

Next steps

  • Print revision C with flat leaves
  • Stiffness measurement
  • Add a micrometer head for repeatable positioning
  • Measure parasitic (unwanted) motion with a second indicator