Glossary

This glossary defines key terms used throughout the LinkForge documentation, Blender integration, and URDF/XACRO standards.

Link

A representation of a rigid body in a robot model. Every link must have a unique name. Links contain properties for Visual, Collision, and Inertial data.

Joint

A connection between two links that defines their relative motion (e.g., revolute, prismatic, fixed, continuous).

Root Link

The base of the robot’s kinematic tree. A robot can only have one root link, and it must not have any parent joint.

Inertia Tensor

A 3x3 matrix representing the rotational inertia of a rigid body. LinkForge simplifies this by calculating the moments of inertia (ixx, iyy, izz) based on the object’s geometry and mass.

Joint Interface

The configuration of how a joint is controlled in ROS 2. Includes Command Interfaces (e.g., Velocity) and State Interfaces (e.g., Position, Velocity).

Sensor

A device that provides feedback from the environment (e.g., Camera, Lidar, IMU). In LinkForge, sensors are specialized Empty objects attached to Links that generate <sensor> tags and their associated Gazebo configurations.

ROS 2 Control

The standard framework for robot control in ROS 2. LinkForge natively supports this by generating the <ros2_control> XML block, mapping joint interfaces (Position, Velocity, Effort) to hardware plugins.

Gazebo

The primary physics simulator for ROS. LinkForge supports both Gazebo Classic (v11) and modern Gazebo Sim (Harmonic/Ionic) by exporting compatible collision geometry and sensor tags.

URDF (Unified Robot Description Format)

An XML format used in ROS to describe the physical properties of a robot.

XACRO (XML Macros)

An XML macro language used to simplify URDF files by allowing variables, math, and macros.

Actuation Vector

The visual representation in Blender showing the direction of force or movement for a specific joint interface.

SRDF (Semantic Robot Description Format)

An XML format used alongside URDF to provide semantic information for motion planning. It defines planning groups, named poses, end effectors, virtual joints, and collision filters. Used primarily by MoveIt and MoveIt 2. LinkForge can generate SRDF files programmatically via SRDFGenerator or the RobotBuilder.export_srdf() helper.

Planning Group

A named subset of links and joints used by MoveIt to plan motion for one part of the robot (e.g., arm, hand). Planning groups are defined in the SRDF and managed through builder.semantic.group() in LinkForge.

Composer (RobotBuilder)

The programmatic Python API for building robots without Blender. RobotBuilder supports two workflows: Macro-Assembly (attaching complete sub-robots) and Micro-Construction (adding individual links and joints with the LinkBuilder fluent API). Produces a unified, validated Robot object ready for both URDF and SRDF export.

Kinematic Graph

An internal graph representation of the robot’s link-joint topology. KinematicGraph is used by the validator to detect cycles, find the root link, and perform topological traversal. Available as a public API for advanced users who need custom graph analysis.