URDF & Xacro Robot Kinematics

ModelScript provides first-class support for URDF (.urdf) and Xacro (.xacro), the robotics industry and ROS (Robot Operating System) standard for describing kinematic trees, inertial properties, visual geometry, and joint limits of robotic manipulators, humanoids, and autonomous vehicles.

---

Capabilities & Supported Formats

Format	Extension	Description
Unified Robot Description Format	.urdf, .xml	XML schema defining kinematic links, joints (revolute, continuous, prismatic, fixed, floating, planar), inertial parameters, collision bounds, and visual meshes.
Xacro Macro Template	.xacro	Parametric XML preprocessor adding variables (<xacro:property>), mathematical expressions, and reusable macros (<xacro:macro>).

Key Architectural Features

• Xacro Expansion & Parser:
  • Robust XML reader with automatic in-memory macro expansion (<xacro:macro>) and mathematical expression evaluation before parsing.
  • Generates strongly typed robot AST representation via parseUrdf().
• Topological Kinematic Tree & Featherstone Algorithms:
  • Traverses joint-link connectivity starting from the root base link.
  • Implements Recursive Newton-Euler Algorithm (RNEA) for inverse dynamics: calculates required joint torques $\mathit{\tau }$ given joint positions $\mathbf{q}$, velocities $\dot{\mathbf{q}}$, and accelerations $\ddot{\mathbf{q}}$.
  • Implements Articulated-Body Algorithm (ABA) for forward dynamics: evaluates forward acceleration $\ddot{\mathbf{q}}=\mathbf{M}(\mathbf{q}{)}^{-1}(\mathit{\tau }-\mathbf{C}(\mathbf{q},\dot{\mathbf{q}})-\mathbf{g}(\mathbf{q}))$ in $O(N)$ operations.
• Robotics Linters (M7501–M7508):
  • Detects dangling parent/child link references, disconnected kinematic sub-trees, inverted joint limits (lower > upper), zero joint axis vectors, missing inertia tags, and non-physical inertia tensors.
• Multi-Target Projections:
  • Modelica MultiBody: Synthesizes Modelica.Mechanics.MultiBody robotic arms with joint friction and actuator controllers.
  • MSC Adams: Exports Adams .adm solver datasets.
  • SIMPACK: Generates SIMPACK .spck mechanisms.
  • 3D CAD: Projects robot geometry into CSG primitives and STEP visual meshes.

---

Command Line Interface (msx urdf)

msx urdf <action> [files...] [options]

Action	Description	Key Options
lint	Runs kinematic tree validation, joint limit checks, and inertia verification.	—
rnea	Evaluates inverse dynamics (RNEA) at test joint coordinates.	--gravity
to-modelica	Generates standard Modelica.Mechanics.MultiBody robot system.	--out=<file.mo>
to-adams	Projects robot mechanism into MSC Adams .adm solver dataset.	--out=<file.adm>
to-simpack	Projects robot mechanism into SIMPACK XML .spck model.	--out=<file.spck>
to-dae	Lowers kinematic state equations directly into DAEBuilder arena.	—

Examples

# Evaluate inverse dynamics (RNEA) at test joint coordinates
msx urdf rnea KukaIiwa14.urdf

# Check for inverted joint limits or dangling parent links
msx urdf lint MobileManipulator.urdf

# Convert robot description into standard Modelica 3.x
msx urdf to-modelica PandaArm.urdf --out=PandaArm.mo

# Export to MSC Adams for vehicle-mounted robot simulation
msx urdf to-adams RoverArm.urdf --out=RoverArm.adm

---

Robotics Linters & Diagnostic Rules

8 rules5 error3 warning Run with msx lint

Code	Rule	Severity	Message
M7501	unresolved-parent-link	error	Joint '<jointName>' references non-existent parent link '<linkName>'.
M7502	kinematic-loop	error	Closed kinematic chain or duplicate parent detected at link '<linkName>' (URDF requires open tree).
M7503	invalid-inertia-tensor	error	Link '<linkName>' defines non-physical inertia tensor: <reason>.
M7504	invalid-joint-limits	error	Joint '<jointName>' defines invalid limits (lower: <lower> >= upper: <upper>).
M7505	missing-mesh-resource	warning	Visual mesh URI '<uri>' on link '<linkName>' may not resolve at runtime.
M7506	massless-link	warning	Link '<linkName>' has zero mass and no inertial specification.
M7507	zero-norm-joint-axis	error	Joint '<jointName>' defines a zero-norm rotation/translation axis [0, 0, 0].
M7508	continuous-joint-with-limits	warning	Joint '<jointName>' is declared 'continuous' but specifies upper/lower limits.

Generated from languages/urdf/src/errors.ts. All languages →