LinuxCNC Tool Correction Panel

Overview

LinuxCNC Tool Correction Panel with LCD display and rotary encoders

This project provides an additional box/panel for machining tool correction in LinuxCNC. It's an extension of the original LinuxCNC_ArduinoConnector project, specifically adapted for tool correction applications.

Important: This software is NOT intended for timing and safety-critical I/O operations. Do not use it for emergency stops or endstop switches.

Features

• Tool shank correction - using rotary encoder
• Tool height correction - using rotary encoder
• LCD display - shows current correction values
• Automatic correction application - before running main machining program
• Correction reset - display automatically resets after application

Hardware Requirements

• Arduino Mega 2560
• 2x rotary encoders (for shank and height correction)
• LCD display 20x4 characters
• USB serial connection between Arduino and LinuxCNC

Installation and Configuration

1. Arduino Software

Upload the firmware from src/ folder to Arduino Mega 2560. The software automatically configures:

• 2 quadrature encoders on pins defined in code
• LCD display for showing correction values
• Serial communication with LinuxCNC

2. LinuxCNC Configuration

2.1 Python Connector Installation

Copy the linuxcnc/arduino-connector.py file to your LinuxCNC system and make it executable:

sudo cp linuxcnc/arduino-connector.py /usr/local/bin/
sudo chmod +x /usr/local/bin/arduino-connector.py

2.2 INI File Configuration

Edit your existing INI file to add the required variables (see linuxcnc/example.ini):

# In the existing [RS274NGC] section, add:
[RS274NGC]
...
HAL_PIN_VARS = 1

# In the existing [HAL] section, add:
[HAL]
TWOPASS = on
...
HALFILE = tool-correction-panel.hal

2.3 HAL Configuration

Copy the linuxcnc/tool-correction-panel.hal file to your LinuxCNC configuration. This file contains:

• Shank correction: Encoder for tool shank correction

  • Encoder connected to arduino.counter.0
  • Output value in corr-drik-enc-diff.out-f
  • Scale: 0.005 (conversion from encoder pulses to mm)

• Height correction: Encoder for tool height correction

  • Encoder connected to arduino.counter.1
  • Output value in corr-vyska-enc-diff.out-f
  • Scale: 0.005 (conversion from encoder pulses to mm)

• Reset signal: Control from G-code using motion.digital-out-03

Usage

1. Setting Corrections

1. Start LinuxCNC with the configured panel
2. LCD display shows current correction values
3. Turn encoders to set desired corrections:
   • Encoder 1: Tool shank correction (X-axis)
   • Encoder 2: Tool height correction (Z-axis)

2. Applying Corrections

Before running your main machining program, call the G-code linuxcnc/apply-correction.ngc:

; Call correction program
O<apply-correction> call

This program automatically:

1. Selects tool T3 and applies basic G43 correction
2. Reads shank correction value from encoder and applies it to the tool
3. Reads height correction value from encoder and applies it to coordinate system
4. Resets values on panel (clears display)

3. G-code for Correction Application

The linuxcnc/apply-correction.ngc file contains:

G8
G90 G94 G18
G21
G54

; Select right tool
T3 M6 G43
G4 P0.5

; Apply correction shank
#<corr_drik> = [#<_hal[corr-drik-enc-diff.out-f]> / 2]
G10 L1 P3 X[#5401 + #<corr_drik>]
G4 P0.1
G43

; Apply correction height
#<corr_vyska> = #<_hal[corr-vyska-enc-diff.out-f]>
G10 L2 P1 Z[#5223 + 0.005]
G4 P0.1
G54

; Reset correction value on panel
M65 P3
G4 P0.1
M64 P3

M2

Technical Details

Communication Protocol

The system uses serial communication with protocol: <Signal><PinNumber>:<PinState>

Relevant signals for correction panel:

• R - Quadrature encoders (arduino → linuxcnc)
• F - Float variables for LCD (linuxcnc → arduino)
• E - Keep-alive signal (bidirectional)

HAL Components

The system uses these HAL components:

• sample_hold: Captures encoder value on reset pulse
• scaled_s32_sums: Calculates relative correction (current - captured value)

Scales and Conversions

• Encoder → mm: 0.005 (200 pulses/revolution, 1mm/revolution)
• LCD precision: 3 decimal places
• Shank correction: Divided by 2 in G-code for finer adjustment

Troubleshooting

Encoders not responding

1. Check encoder connections to Arduino:
   • Encoder 0 (shank correction): Connect A signal to pin A3, B signal to pin 10
   • Encoder 1 (height correction): Connect A signal to pin 11, B signal to pin 12
   • Use interrupt-capable pins for best performance (see Arduino Mega interrupt pins: 2, 3, 18, 19, 20, 21)
2. Verify configuration in arduino-connector.py:

   QuadEncs = 2
   QuadEncSig = [2,2]  # Signal type 2 = position signal (for MPG wheel)

3. Check pin definitions in src/main.cpp:

   Encoder Encoder0(A3,10);    // Encoder 0: A signal on A3, B signal on pin 10
   Encoder Encoder1(11,12);    // Encoder 1: A signal on pin 11, B signal on pin 12

4. Verify encoder power supply (typically 5V) and ground connections
5. Check encoder pulse multiplier settings:

   const int QuadEncMp[] = {4,4};  // 4 electrical impulses per mechanical pulse

LCD not displaying values

1. Check LCD variable settings:

   LcdFloatVars = 2

2. Verify HAL connections in tool-correction-panel.hal

G-code not working

1. Check that HAL_PIN_VARS = 1 is set in INI file
2. Verify correct HAL file is loaded
3. Check tool number (T3) in correction G-code

Original Project

This project is based on LinuxCNC_ArduinoConnector by Alexander Richter.

The original README with complete Arduino connector documentation is available in the git history of this project.

License

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.