Compliance estimation and structural observability
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Purpose
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- Estimate quasi-static structural behavior under load
- Detect excessive compliance that risks tolerance loss
- Provide slow-varying state information for process supervision
- Not intended for real-time control loops

Tilt estimation
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- Derived from accelerometer data
- Uses gravity vector for orientation reference
- Strong low-pass filtering applied
- Valid only in quasi-static conditions
- Used to estimate spindle plate rotation under load

Strain gauge measurement
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- Strain gauge mounted on X carriage
- Measures bending of X gantry under load
- Acts as cutting-force proxy
- Provides information independent of vibration measurements

Motor current as load proxy
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- Motor current monitored at spindle drive
- Two components used:

  - fast component:
    - incipient stall detection
  - slow envelope:
    - mean cutting load estimation

Compliance model
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- Structural compliance model maintained in ECU
- Model inputs:

  - spindle plate tilt
  - X-carriage strain
  - motor current
- Model output:

  - estimated tool/spindle deflection envelope
- Model characteristics:

  - calibrated using known static or quasi-static loads
  - evaluated only in steady-state conditions
  - versioned and recalibratable
- Model is:

  - a slow observer
  - not part of safety system