CNC Mill Concept: Piezo Shunt Damping

Introduction

This post is part of the CNC Mill Concept hub. It covers the electromechanical damping strategy for the machine: piezo ceramic shunt damping applied to the spindle tower, the shunt network design, instrumentation for power dissipation measurement, and the optional adaptive tuning loop.

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

License

This project (with exceptions) is published under the CC Attribution-ShareAlike 4.0 International License.