Using the Touchprobe

Deprecated Module: This module is no longer supported and is not compiled in by default. If someone fixes this, please let us know. This documentation is left here for historical purposes. Alternative: For modern probing functionality, see the ZProbe module which is actively maintained and supports more features.

About Touchprobes

Touchprobe

Example of a CNC touchprobe

Currently, the only operation regarding touchprobes supported by this module is G31.

G31 works similarly to G1 codes but stops if the probe is touched.

Important limitation: Coordinated moves are not supported.

This means only moves along a single axis will work.

Basic Usage Examples

Simple Probe Move

This will move to Z-10 and stop when a touch happens during that move:

G90
G31 Z-10 F150
  • G90 - Absolute positioning mode
  • G31 - Probe move command
  • Z-10 - Move to Z position -10
  • F150 - Feed rate of 150 mm/min

Two-Stage Probe (Fast then Slow)

This will probe at a fast speed, retract, probe at a slow speed, and report the position:

G91
G31 Z-10 F300
G0 Z0.2
G31 Z-0.3 F50
M114

What each line does:

  • G91 - Switch to relative positioning
  • G31 Z-10 F300 - Fast probe down 10mm at 300 mm/min
  • G0 Z0.2 - Retract 0.2mm
  • G31 Z-0.3 F50 - Slow probe down 0.3mm at 50 mm/min
  • M114 - Report current position

In addition to the M114 report, every touch is logged to a file if logging is enabled (see Configuration section below).

Configuration

The touchprobe module has the following configuration values (the values shown are defaults):

touchprobe_enable                   false              # enables/disables the module (other values ignored if false)
touchprobe_log_enable               false              # should the touches be logged to file
touchprobe_logfile_name             /sd/probe_log.csv  # location of the log file
touchprobe_log_rotate_mcode         0                  # adds a spacer to logfile if Mxxx is issued
touchprobe_pin                      nc                 # selects the pin where the probe is connected
touchprobe_debounce_count           100                # reports touch if probe active for this many ticks (prevents false positives)

Configuration Details

Parameter Description
touchprobe_enable Must be set to true to use the module
touchprobe_log_enable Set to true to log all probe touches
touchprobe_logfile_name Path to log file (must be on SD card)
touchprobe_log_rotate_mcode M-code number to insert spacer in log
touchprobe_pin Input pin for probe signal
touchprobe_debounce_count Higher values = more noise resistance but slower response

Using Log Files

The log file is an easy way to create point clouds of the probed objects.

Important Setup Steps:
  • Due to bugs in mbed, the log file isn't created automatically
  • You must create the file first and restart Smoothie to update the file-handle properly
  • Properly unmount (safely remove) the SD card before logging
  • The file-system is dual-mounted by your OS and Smoothie, which can cause desynchronization

If you forget to safely remove the SD card, try to remount it afterward.

Most of the time, no data loss will happen.

Convert to Stanford PLY File

It’s very easy to convert the logfile to a PLY file, which is supported by most point cloud applications.

Note: This only works if there are no spacers in the file that are generated by the “log-rotation” M-code.

Conversion Steps

  1. Count the points - Find out how many points have been logged
    • On Linux/Mac: Use wc -l filename.csv
    • On Windows: Open in a text editor and check line count
  2. Create the PLY header: 
    ply
format ascii 1.0
comment smoothie cloud
element vertex xxxxxxxx
property float x
property float y
property float z
element face 0
property list uchar int vertex_indices
end_header

  3. Replace xxxxxxxx with the number you found in step 1

  4. Prepend the header to your log file data

  5. Save with .ply extension

  6. You’re done! Open in any point cloud viewer

Finding the Center of Round Objects

A common CNC task is finding the center of circular holes or bosses.

Method

Finding center of round objects

Diagram showing probe points for finding center

Steps

  1. Probe along the Y-axis for P1 and P2 (opposite sides)

  2. Calculate the center between them:

    P3 = (P1.x, P1.y + (P2.y - P1.y) / 2)

  3. Probe along the X-axis for P4 and P5
    • Make sure the Y-axis is positioned at P3.y

  4. Calculate the center between them:

    M = (P4.x + (P5.x - P4.x) / 2, P3.y)

  5. M is the center of the round object

Alternatives

Since this module is deprecated, consider using:

Further Reading