Control electronics and PCB architecture

Purpose

• Provide a clear separation between:

  • motion control

  • process supervision

  • sensing and data acquisition

  • safety

• Enable extensible, modular sensing and supervision

• Avoid tight coupling between motion execution and adaptive logic

ECU (master PCB)

• Acts as real-time supervisory controller

• Responsibilities:

  • sensor fusion

  • machine state estimation

  • process supervision decisions

• Interfaces:

  • CAN-FD:

    • communication with distributed sensor PCBs

  • RS-485:

    • communication with spindle servo drive

  • GPIO:

    • low-latency triggering of Duet macros

  • SPI or UART:

    • communication with Raspberry Pi

• Does not:

  • generate motion trajectories

  • directly drive axes

  • participate in safety chain

Distributed sensor PCBs

• Zonal architecture:

  • multiple PCBs placed near sensors

• Connected to ECU via CAN-FD

• Responsibilities:

  • sensor signal acquisition

  • local filtering

  • FFT and envelope extraction

  • threshold detection

• Communication behavior:

  • event-driven data transmission

  • periodic heartbeat messages

• Fault handling:

  • ECU detects missing heartbeats

  • missing data treated as sensor failure

• Debug and validation:

  • raw data access via USB or SPI

Communication architecture

• CAN-FD used for:

  • robust, deterministic sensor data exchange

• SPI / UART used for:

  • configuration

  • logging

  • visualization

• GPIO used for:

  • low-latency supervisory actions

  • feed and spindle-related macros

Raspberry Pi integration

• Runs Duet services and web interface

• Hosts plugins for:

  • configuration of ECU and sensor PCBs

  • data logging

  • visualization (e.g. Grafana)

• Not used for:

  • real-time control

  • safety-critical functions

Sensor PCB Capabilities

General Architecture

Two identical distributed sensor PCBs are used.

• Mounted close to structural measurement locations.

• Based on an STM32G4 (CAN-FD capable).

• CAN-FD communication to the main ECU.

• Optional synchronization line for deterministic simultaneous sampling.

• Careful separation of analog and digital domains.

All nodes share the same CAN-FD bus. The ECU is located at one physical end of the bus.

CAN Topology Overview

        flowchart LR
%% --- CAN participants forced horizontal ---
subgraph CAN_BUS
  direction LR

  ECU["ECU
  Main Controller
  CAN-FD"]

  SN_A["Sensor Node A
  Left X-Beam"]

  SN_B["Sensor Node B
  Right X-Beam"]

  ECU ---|CAN-FD Bus| SN_A ---|CAN-FD Bus| SN_B
end


%% --- Node B sensors (ABOVE SN_B) ---
DMS_R["X-Beam DMS - Right
Beam bending
Dynamic load estimation"]

ACC_T["Tower Accelerometer
Structural vibration"]

MIC_T["Tower Microphone
Structural acoustics"]

TEMP_T["Tower Temperature
Structural temperature"]

DMS_R --> SN_B
ACC_T --> SN_B
MIC_T --> SN_B
TEMP_T --> SN_B


%% --- Node A sensors (BELOW SN_A) ---
DMS_L["X-Beam DMS - Left
Beam bending
Dynamic load estimation"]

ACC_SP["Spindle Plate Accelerometer
Vibration + Low-freq tilt"]

MIC_SP["Spindle Housing Microphone
Bearing and chatter acoustics"]

TEMP_SP["Spindle Housing Temperature
Thermal growth monitoring"]

DMS_L --> SN_A
ACC_SP --> SN_A
MIC_SP --> SN_A
TEMP_SP -->SN_A
    

Strain Gauge Interface

• Supports multiple full-bridge configurations.

• External 24-bit ADC recommended for dynamic strain measurement.

• Differential low-noise instrumentation front-end.

• Bridge excitation provided by PCB.

• Shielded differential wiring to remote DMS.

Typical usage:

• 2 × X-beam full bridges.

Accelerometer Interface

• SPI interface for digital 3-axis accelerometers.

• Deterministic sampling capability.

• Remote mounting via short shielded cable or rigid daughterboard.

• Optional synchronization between PCBs.

Typical usage:

• 1 × spindle plate accelerometer.

• 1 × tower accelerometer.

Microphone Interface (Piezo Surface Microphone)

• High-impedance charge amplifier front-end.

• Anti-alias filtering.

• Analog input to ADC.

• Shielded cable required.

Typical usage:

• 1 × spindle housing microphone.

• 1 × tower microphone.

Temperature Sensor Interface

• SPI/I²C thermocouple frontend or RTD interface.

• Alternatively precision analog temperature input.

• Slow sampling rate sufficient.

Typical usage:

• 1 × spindle housing temperature.

• 1 × tower plate temperature.

Piezo Shunt Communication Interface

• SPI or I²C master interface.

• Used to communicate with external piezo shunt PCBs.

• No high-voltage circuitry on the sensor PCB.

• Digital control and monitoring only.