Electromechanical damping: piezo shunt damping
==============================================

Purpose and scope
-----------------

- Piezo elements used exclusively for **structural damping**
- Function:

  - convert mechanical strain energy into electrical energy
  - dissipate energy in passive or semi-passive shunt networks
- Piezo damping elements are **not used as sensors**
- Sensing using piezo surface microphones is handled separately

Piezo damping elements
----------------------

- Type:

  - piezo ceramic disks (PZT)
- Mounting:

  - bonded directly to steel structure
- Placement strategy:

  - bonded at **modal antinodes** of the spindle tower
  - placement determined by:
  - 
    - modal analysis
    - experimental hammer testing
- Number:

  - multiple elements distributed over dominant bending modes
- Explicit locations:

  - spindle tower side plates
- Not placed on:

  - spindle housing
  - spindle mounting plate
  - non-load-bearing panels

Shunt networks
--------------

- Each piezo element connected to an electrical shunt
- Shunt types:

  - resistive (R)
  - resistive-inductive (R-L), if required
- Baseline damping:

  - passive
  - independent of software
- Failure behavior:

  - defaults to fixed, known-good resistance

Instrumentation of shunts
-------------------------

- Shunt circuits instrumented with:

  - piezo voltage measurement
  - piezo current measurement
- ECU computes:

  - instantaneous electrical power
  - averaged dissipated power
- Power data:

  - logged
  - visualized
  - used for tuning and validation

Adaptive shunt tuning
---------------------

- Shunt resistance adjustable via digital potentiometer
- Tuning strategy:

  - slow supervisory loop
  - time scale: minutes
- Algorithm characteristics:

  - small bounded resistance steps
  - comparison of dissipated power at neighboring settings
  - hysteresis and min/max limits
- Purpose:

  - compensate for:
  
    - temperature changes
    - boundary-condition changes
    - structural aging
- Adaptive tuning:

  - optional
  - fully disable-able
  - not required for baseline damping

Interaction with other damping strategies
-----------------------------------------

- Piezo shunt damping complements:

  - structural CLD (carbon fiber)
  - internal damping (epoxy granite)
- Piezo damping targets:

  - specific structural modes
- Not intended to:

  - replace passive damping
  - provide active vibration cancellation