Step 3 — Proportional Control Correction

The error map from Step 2 is fed into a proportional controller that adjusts the G-code feedrates for the next layer to compensate for measured surface-height deviations. This closes the control loop.

Control Law

F_corrected = F_nominal * (1 + K_p * z_err_mm)

Where:

• F_nominal — the feedrate in the original (uncorrected) G-code for the next layer.
• K_p — proportional gain (default: 1.0). Tuned experimentally.
• z_err_mm — the surface height error at the nearest measured point from the previous layer’s error map.

Intuition

• Positive error (surface too high) → increase feedrate → robot moves faster → deposits less material → surface drops.
• Negative error (surface too low) → decrease feedrate → robot moves slower → deposits more material → surface rises.

Spatial Matching

For each extruding G-code point (E > 0) in the next layer’s toolpath, the controller finds the nearest point in the error map CSV (by 3D Euclidean distance) and applies that point’s err_mm value to the feedrate formula. Only extruding moves are modified; travel moves are passed through unchanged.

Command

uv run python simple_proportional.py \
  <next_layer.gcode> \
  <L<N>_error_map.csv> \
  -k <K_p> \
  -o <next_layer_corrected.gcode>

Working directory: ros2_ws/lib/control/simple_proportional/

Arguments

Flag	Default	Purpose
Positional 1	—	Next layer’s nominal G-code file
Positional 2	—	Previous layer’s error_map.csv
-k, --proportional_constant	1.0	Proportional gain K_p
-o	—	Output path for corrected G-code
--lower_bounds_corrected_feed	3.2	Minimum allowed corrected feedrate
--preview	—	Generate an HTML 3D plot of the feedrate corrections (path auto-derived if flag given without value)

Inputs

1. Next Layer G-Code (nominal)

Standard slicer output. Only G1 moves with non-zero E values have their F parameter adjusted.

G1 X-7.119 Y-17.261 E24.0 F3.4 ;N4
G1 X-5.676 Y-16.964 E24.0 F3.4 ;N5

2. Previous Layer Error Map (CSV)

X,Y,Z,err_mm
12.2021,47.3637,43.2479,4.0644
10.7972,47.6810,43.2649,4.0644

Output

A corrected G-code file identical to the input except that feedrate (F) values on extruding moves have been scaled according to the control law. This file becomes the input to Step 1 for the next iteration.

Future Work

The current controller is purely proportional (P-only). Planned extensions include:

• Integral (I) term — accumulate historical error across multiple layers to eliminate steady-state offset.
• Derivative (D) term — respond to the rate of error change between consecutive layers.
• Full PID tuning with per-region gain scheduling.