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We of the LinuxCNC project hope that you will share your changes with us, so that the community can benefit from your work. Github makes this sharing very easy: after you polish your changes and push them to your github fork, send us a Pull Request.
Code Notes
Intended audience
This document is a collection of notes about the internals of LinuxCNC. It is primarily of interest to developers, however much of the information here may also be of interest to system integrators and others who are simply curious about how LinuxCNC works. Much of this information is now outdated and has never been reviewed for accuracy.
Organization
There will be a chapter for each of the major components of LinuxCNC, as well as chapter(s) covering how they work together. This document is very much a work in progress, and its layout may change in the future.
Terms and definitions
'AXIS' - An axis is one of the nine degrees of freedom that define a tool position in three-dimensional Cartesian space. Those nine axes are referred to as X, Y, Z, A, B, C, U, V, and W. The linear orthogonal coordinates X, Y, and Z determine where the tip of the tool is positioned. The angular coordinates A, B, and C determine the tool orientation. A second set of linear orthogonal coordinates U, V, and W allows tool motion (typically for cutting actions) relative to the previously offset and rotated axes. Unfortunately "axis" is also sometimes used to mean a degree of freedom of the machine itself, such as the saddle, table, or quill of a Bridgeport type milling machine. On a Bridgeport this causes no confusion, since movement of the table directly corresponds to movement along the X axis. However, the shoulder and elbow joints of a robot arm and the linear actuators of a hexapod do not correspond to movement along any Cartesian axis, and in general it is important to make the distinction between the Cartesian axes and the machine degrees of freedom. In this document, the latter will be called 'joints', not axes. The GUIs and some other parts of the code may not always follow this distinction, but the internals of the motion controller do.
'JOINT' - A joint is one of the movable parts of the machine. Joints are distinct from axes, although the two terms are sometimes (mis)used to mean the same thing. In LinuxCNC, a joint is a physical thing that can be moved, not a coordinate in space. For example, the quill, knee, saddle, and table of a Bridgeport mill are all joints. The shoulder, elbow, and wrist of a robot arm are joints, as are the linear actuators of a hexapod. Every joint has a motor or actuator of some type associated with it. Joints do not necessarily correspond to the X, Y, and Z axes, although for machines with trivial kinematics that may be the case. Even on those machines, joint position and axis position are fundamentally different things. In this document, the terms 'joint' and 'axis' are used carefully to respect their distinct meanings. Unfortunately that isn't necessarily true everywhere else. In particular, GUIs for machines with trivial kinematics may gloss over or completely hide the distinction between joints and axes. In addition, the INI file uses the term 'axis' for data that would more accurately be described as joint data, such as input and output scaling, etc.
This distinction was made in version 2.8 of LinuxCNC. The INI file got a new section [JOINT_<num>]. Many of the parameters that were previously proper to the [AXIS_<letter>] section are now in the new section. Other sections, such as [KINS], also take on new parameters to match this. An update script has been provided to transform old INI files to the new axes/joints configuration.
'POSE' - A pose is a fully specified position in 3D Cartesian space. In the LinuxCNC motion controller, when we refer to a pose we mean an EmcPose structure, containing six linear coordinates (X, Y, Z, U, V, and W) and three angular ones (A, B, and C).

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  1. LinuxCNC
  2. LinuxCNC Documentation
  3. English
There will be a chapter for each of the major components of LinuxCNC, as well as chapter(s) covering how they work together. This document is very much a work in progress, and its layout may change in the future.
There will be a chapter for each of the major components of LinuxCNC, as well as chapter(s) covering how they work together. This document is very much a work in progress, and its layout may change in the future.
a year ago
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Source string description
type: Plain text
Flags
ignore-begin-space, ignore-end-space, read-only
Source string location
src/code/code-notes.adoc:26
String age
a year ago
Last updated
12 months ago
Source string age
a year ago
Translation file
docs/po/documentation.pot, string 580