Metrology and in-process measurement
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Purpose
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- Establish accurate knowledge of tool geometry
- Reduce uncertainty from tool runout and length variation
- Enable high repeatability without relying on conservative margins
- Decouple accuracy from spindle and tool holder quality

Laser-based tool measurement
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- Dedicated laser emitter and receiver
- Emitter and receiver housed separately
- Optical aperture implemented as a slit:

  - width: 5-10 µm
- Measurement performed with spindle rotating

Measurement procedure
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- Spindle moves tool into laser beam
- Initial detection:

  - threshold-based (not binary light/no-light)
- Secondary fine measurement:

  - sensor housing mounted on precision flexure
  - flexure actuated independently of machine motion
- Flexure motion resolution:

  - sub-100 nm repeatability
- Tool remains rotating during measurement

Measured quantities
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- Tool length
- Effective tool diameter
- Radial runout envelope
- Repeatable reference position for tool geometry

Thermal stabilization
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- Laser emitter and sensor actively heated
- Target temperature: fixed elevated setpoint (e.g. 50 °C)
- Measurement only enabled once thermal equilibrium is reached
- Thermal history not used for compensation
- Stability prioritized over absolute temperature accuracy

Calibration strategy
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- All absolute values obtained through calibration
- Measurement system optimized for:

  - repeatability
  - consistency
- Absolute accuracy derived from:

  - known calibration artifacts
  - reference tools

Integration
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- Measurement system treated as a metrology subsystem
- Not part of:

  - force loop
  - vibration control
- Results communicated to:

  - Raspberry Pi (tool library management)
  - Duet (tool offsets)
- Compatible with:

  - manual tool changes
  - future automated tool handling

Scope limitations
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- No real-time tool deflection measurement
- No thermal growth compensation of tool during cutting
- No wear prediction or life estimation