Machine state estimation and process supervision
================================================

Purpose
-------

- Combine sensor data into a coherent machine state
- Supervise the machining process based on estimated state
- Prevent tolerance loss, chatter, and spindle stall
- Never perform motion planning or trajectory generation

Machine state estimation
------------------------

- State estimation performed in ECU
- Inputs:

  - vibration:

    - piezo surface microphones
    - accelerometers
  - quasi-static tilt:

    - low-pass-filtered accelerometer data
  - structural load:

    - X-carriage strain gauge
  - spindle load:

    - motor current
- Sensor fusion performed with explicit time-scale separation:

  - fast signals:

    - vibration
    - chatter indicators
  - slow signals:

    - tilt
    - strain
    - motor current envelope

Machine state classification
----------------------------

- ECU classifies the current operating state as:

  - normal operation
  - static overload / excessive compliance
  - dynamic instability (chatter)
  - incipient spindle stall

Process supervision actions
---------------------------

- ECU supervises process only
- ECU does not:

  - control axis motion
  - modify trajectories
  - override safety systems
- Actions requested via:

  - Duet macros
  - GPIO signals for low latency

Supervision logic
-----------------

- Static overload / excessive compliance:

  - detected by increased tilt and/or strain
  - action: reduce feed rate
- Dynamic instability (chatter):

  - detected by elevated vibration energy
  - action: adaptive spindle speed adjustment
- Incipient stall:

  - detected by rapid motor current increase
  - action: immediate feed reduction

State transitions and hysteresis
--------------------------------

- State transitions implemented using Schmitt-trigger logic
- Upper threshold:

  - spindle motor current ≥ 100 % rated
  - transition to reduced-feed state
- Lower threshold:

  - spindle motor current ≤ configurable value (e.g. 80 %)
  - maintained for configurable time
  - transition back to normal-feed state
- Hysteresis prevents oscillation and hunting

Configuration and scope
-----------------------

- All thresholds and timing parameters:

  - configurable via Raspberry Pi plugin
  - logged for analysis
- Supervisory logic:

  - non-safety-critical
  - fully disable-able
  - degrades gracefully if unavailable
- Safety functions remain hardware-only and independent

.. graphviz::

  digraph CNC_Supervision {
    rankdir=TB;
    compound=true;
    fontsize=12;
    ranksep=1.2;
    splines=true;
    labelloc="t";
    label="CNC State Estimation, Compliance Supervision and Chatter Control Architecture";

    node [shape=box, style=rounded];

    /* =======================
       SENSOR LAYER
       ======================= */

    subgraph cluster_sensors {
        label="Sensors";
        style=dashed;

        subgraph cluster_slow {
            label="Slow Domain (Hz)";
            style=dashed;
            
            accel_plate_slow     [label="Accelerometer\n(Spindle Plate Angle)"];
            accel_tower_slow     [label="Accelerometer\n(Tower, reference)"];
            motor_current   [label="Motor Current\n(RS-485)"];
            
        }
        subgraph cluster_fast {
            label="Fast Domain (kHz)";
            style=dashed;
            
            piezo_housing   [label="Piezo\n(Spindle Housing)"];
            piezo_tower     [label="Piezo\n(Tower)"];
            accel_plate     [label="Accelerometer\n(Spindle Plate)"];
            accel_tower     [label="Accelerometer\n(Tower)"];
            strain_x        [label="Strain Gauges\n(X Beams)"];
        }
        
    }


    /* =======================
       ECU
       ======================= */

    subgraph cluster_ecu {
        label="ECU (Master PCB)";
        style=bold;

        /* SLOW DOMAIN */
        

            // tilt_est        [label="Tilt Estimation\n(Low-pass Accel)"];
            // strain_eval     [label="Strain Evaluation"];
            // {
            //     rank=same;
            //     tilt_est;
            //     strain_eval;
            subgraph cluster_compliance {
                label="Compliance Model";
                style=dashed;
                
                tilt_model[label="Tilt Estimate"];
                compliance_model[label="Compliance Model\n(Deflection Estimate)"];
                {
                    rank=same;
                    tilt_model;
                    compliance_model;
                }
            }
            
            // compliance_model[label="Compliance Model\n(Deflection Estimate)"];
            // tilt_model[label="Tilt Estimate"];
            
            chatter_metric [label="Chatter Detection"];
            stall_detect   [label="Incipient Stall Detection"];


        /* DECISION LAYER */
        
        decision_layer [label="State Classification & Hysteresis\n\nStates:\n- Normal\n- Compliance Overload\n- Chatter\n- Stall"];

        {
            rank=same;
            chatter_metric;
            decision_layer;
        }
    }

    /* =======================
       EXTERNAL CONTROLLERS
       ======================= */

    duet    [label="Duet 3 6HC\n(Motion Control)"];
    spindle [label="Spindle Servo Drive"];

    /* =======================
       CONNECTIONS
       ======================= */

    /* Sensors to preprocessing */
    piezo_housing -> chatter_metric;
    piezo_tower -> chatter_metric;
    accel_plate   -> compliance_model [lhead=cluster_compliance];
    accel_tower   -> compliance_model [lhead=cluster_compliance];
    
    // accel_tower   -> chatter_metric;
    // accel_plate -> chatter_metric;
    
    strain_x    -> compliance_model [lhead=cluster_compliance];
    
    
    
    motor_current -> stall_detect;
    motor_current -> tilt_model  [lhead=cluster_compliance];
    

    /* Domains to decision */
    chatter_metric  -> decision_layer;
    tilt_model  -> decision_layer;
    stall_detect    -> decision_layer;
    compliance_model -> decision_layer;
    tilt_model -> compliance_model;
    
    accel_tower_slow -> tilt_model [lhead=cluster_compliance];
    accel_plate_slow -> tilt_model [lhead=cluster_compliance];
    
    
    /* Outputs */
    decision_layer -> duet    [label="GPIO:\nFeed Reduce\nFeed Restore"];
    chatter_metric -> spindle [label="RS-485:\nRPM Shift"];
    
    {
        rank=same;
        duet;
        spindle;
    }
  }