Vibration and sensing strategy
==============================

Purpose
-------

- Observe machine dynamic and quasi-static behavior
- Detect chatter and dynamic instability
- Provide inputs for compliance estimation and process supervision
- Favor redundant, inexpensive sensing over sparse instrumentation

Piezo surface microphones (sensing only)
-----------------------------------------

- High-impedance piezo elements used exclusively for sensing
- No electrical shunt damping attached
- Used for:

  - high-bandwidth vibration measurement
  - chatter detection
- Non-directional measurement

Explicit placement:

- multiple microphones on spindle tower plates
- one microphone mounted directly on the spindle housing
- additional microphones permitted elsewhere as needed

Notes:

- microphones are distinct from piezo damping elements
- microphones are not bonded at modal antinodes by requirement

Accelerometers
--------------

- Triaxial MEMS accelerometers
- Directional vibration measurement (X, Y, Z)
- Used for:

  - modal analysis and validation
  - directional vibration insight
  - quasi-static tilt estimation

Explicit placement:

- spindle tower
- spindle mounting plate
- optional additional locations where useful

Dual-use strategy:

- high-rate data:

  - vibration analysis
  - frequency-domain features
- strongly low-pass-filtered data:

  - tilt estimation relative to gravity
  - quasi-static deflection observation

Other sensors (contextual)
--------------------------

- Temperature sensors:

  - monitor structural and spindle-related temperatures
  - provide context for drift and boundary-condition changes
- Sensors are not used for real-time compensation in this phase

Integration
-----------

- Sensors connected to distributed sensor PCBs
- Local preprocessing performed on sensor PCBs:

  - filtering
  - FFT or envelope extraction
- Event-driven reporting to ECU via CAN-FD
- Raw data access available for debugging and validation

Sensor Placement and Measurement Coverage
==========================================

Sensor PCB Placement
--------------------

Two identical sensor PCBs are used in the machine.

- **PCB A**  
  Mounted on the left X-beam near the spindle tower.

- **PCB B**  
  Mounted on the right X-beam near the spindle tower.

Both boards use identical hardware and firmware.

The distributed placement reduces analog wiring length for strain gauges
and improves signal integrity. An optional synchronization line between
the boards allows deterministic simultaneous sampling.


X-Beam Instrumentation
----------------------

Strain Gauges (DMS)
^^^^^^^^^^^^^^^^^^^

- One full bridge on the left beam (top and bottom surface).
- One full bridge on the right beam (top and bottom surface).
- Dynamic capable measurement.

Purpose:

- Measure beam bending.
- Support dynamic load estimation.
- Enable structural excitation analysis and compliance observation.

These sensors are intended for both static and dynamic evaluation of the
machine structure.


Spindle Plate Instrumentation
-----------------------------

Accelerometer #1
^^^^^^^^^^^^^^^^

- Mounted directly on the spindle plate.
- Used for high-frequency vibration measurement.
- Supports low-frequency tilt estimation.


Spindle Housing Instrumentation
-------------------------------

Microphone #1
^^^^^^^^^^^^^

- Mounted on the spindle housing.
- Used for bearing and chatter acoustic monitoring.

Temperature Sensor #1
^^^^^^^^^^^^^^^^^^^^^^

- Mounted on the spindle housing.
- Used to monitor spindle thermal growth.


Tower Instrumentation
---------------------

Microphone #2
^^^^^^^^^^^^^

- Mounted on the tower structure.
- Used for structural acoustic monitoring.

Accelerometer #2
^^^^^^^^^^^^^^^^

- Mounted on the tower body.
- Measures tower structural vibration.

Temperature Sensor #2
^^^^^^^^^^^^^^^^^^^^^^

- Installed in a drilled, thermally coupled pocket inside the tower plate.
- Used for structural temperature monitoring.


Measurement Coverage
--------------------

The sensing system provides coverage of:

- Beam static and dynamic bending.
- Spindle plate vibration and tilt.
- Bearing and chatter acoustics.
- Tower structural vibration.
- Spindle thermal growth.
- Tower structural temperature.
- Digital monitoring of piezo shunt circuits.