Compact Design of a Precision XY Positioning Stage

A compact XY stage concept for wafer positioning.

My role Architecture, CAD, FEA, and metrology integration.

Precision mechanics
Parametric CAD
FEA
Metrology

Instrumented common-platen XY stage CAD with air-bearing supports, payload, optical references, and temporary qualification hardware. — Instrumented CAD · computational design study

100 × 100 mmRequired XY workspace

2 kgDesign payload

≤1 µmSettled-position target per axis

01 / ENGINEERING PROBLEM

Research objective

This research began with UBC’s Mechatronics & Instrumentation Group’s need to explore a compact stage for wafer positioning. I investigated a design with 100 mm of travel on each axis, a 2 kg payload, and a 1 µm positioning target per axis. The main challenge was limiting structural and measurement errors at a point 25 mm above the mounting face.

02 / METHODS & ANALYSIS

Design and analysis

CAD and simulation results
Click any figure to enlarge

Design evolution from the serial XY stage through paired-encoder optimization to a common air-bearing platen. — The optimized stacked stage predicted 1.7 / 1.1 µm structural error against a 0.25 µm allocation. Stiffness diagnostics identified both guide compliance and the carried structure as limitations.

Stacked stage

Passive yaw restraint; heavier carried assembly and accumulated compliance.

Planar stage

Lower mass and shorter load path; active yaw, pneumatics, and a larger reference frame.

Detailed underside CAD showing the air-bearing mounts, rotor, and platen load paths. — I reduced the platform mass by approximately 500 g while keeping material around the bearing and motor mounts. FEA compared deformation and flexible modes across payload and bearing-stiffness cases; the plots show bending and a normalized mode shape.

CalculiX fine-mesh platen bending under ax = +5 and ay = −5 meters per second squared, and a normalized 279.2 Hz flexible mode. — I reduced the platform mass by approximately 500 g while keeping material around the bearing and motor mounts. FEA compared deformation and flexible modes across payload and bearing-stiffness cases; the plots show bending and a normalized mode shape.

I also added sensors and mounts in CAD to assess their effect on mass, clearance, and future performance testing.

03 / RESULTS & OUTCOME

Preliminary results

SIMULATED · HARDWARE UNTESTED

0.21 / 0.22 µmX/Y acceleration-only error · assumed supports

320 HzNominal flexible mode

4.6 kgNominal moving mass

39-51 msClean settling: 15/15 within 100 ms

Testing next

BearingsStiffness and load sharing.
StructureCompliance and modes.
PositioningAccuracy, repeatability, and drift.

Disturbance-free cases used model-aware feedforward and 20% force headroom. Disturbed cases took 160–440 ms, exceeding 100 ms; disturbance rejection needs further research. Package target remains unmet.

Preliminary sensor impact

Added mass: +87 g
Conservative margin to 5 kg: 110 → 23 g
Clearance: ±63 mm reserve

CAD estimates; dynamic effects untested.