Overview

In the Mechanical Design Project course (4GC10) at TU Eindhoven, our small team designed and built a Precision Kinematic Mounting (PKM) system for steering a mirror in a LASER communication satellite. The mechanism needed to achieve high-precision beam alignment using only mechanical adjustments — no electronics or motors — through flexure-based transmission with fine-tuning capability.

Full Report — Precision Mirror Steering Mechanism

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Design Concept

The system consists of three modular assemblies:

Structure — A 150 mm x 400 mm x 240 mm enclosure with laser-cut faces glued at edges, featuring a maintenance access hole with doubler plates for stiffness retention
Mirror Steering Mechanism (PKM) — Two flexure assemblies with transmission ratios, operated by bolts with dials for precise positioning. Dimensions: 101 mm x 80 mm x 106 mm
Mirror Mount — Connects the mirror to the flexure output stages

Flexure Design

Flexures were chosen for the small displacements required, providing:

Zero friction — no stick-slip or backlash
No wear — monolithic elastic deformation
Deterministic motion — compliant in desired DOFs, stiff in all others

The transmission ratio was designed to be very small, allowing large dial rotations to produce tiny mirror adjustments without reducing the total stroke. I iterated through several flexure topologies including notch flexures, toroidal flexures, and parallel guiding mechanisms before settling on a modular design that could be 3D printed and tested independently.

Design Iteration

The original actuation concept used strings, but this was rejected due to material constraints. I redesigned the entire mechanism from scratch using rigid beams with notch flexures, incorporating:

Tongue-and-groove joints for assembly
Rubber band preloading for backlash elimination
Lever-based transmission for fine adjustment

Prototyping and Testing

The prototype was manufactured at TU/e's Innovation Space using:

3D printing (PLA, with careful attention to layer/fiber orientation for flexure fatigue life)
Laser cutting for the structural panels

During testing, we identified 5 design shortcomings (toroidal flexure thickness, actuation rod stiffness, mounting rod length, hex nut dimensions, press-fit block sizing) and iterated on each. I also designed and built a custom wooden test rig from scratch when the initial test setup proved too compliant for meaningful measurements.

What I Learned

This project was my deepest dive into precision engineering. The gap between a CAD model and a working prototype is significant — 3D print fiber orientation affects flexure behavior, press-fit tolerances are unforgiving, and testing setups must be stiffer than the device under test. Learning to identify and fix shortcomings systematically was as valuable as the initial design work.

Precision Mirror Steering for LASER Satellite Communication