URDF

Universial Robot Description File to describe robot in ROS.

1. title are elements, and list item are attributes.
2. <> is also elements.

robot

Root element of a urdf file. All other elements should be contained in this element.

• name: the name of robot

link

Describe a rigid body with an inertia, visaual features, and collision properties.

• name: the name of joint

visual

This element specifies the shape of the object for visualization purpose. Multiple instance can exists and the union of the geometry forms the visual representation of the link.

• name: the name of link’s geometry

• origin

  The reference frame of the visual element with respect to the reference frame of the link. Default is same as frame of the link.

  • xyz: represents the x,y,z offset, default is zero vector.
  • rpy: represents the fixed axis roll, pitch and yaw angles in radians.

• geometry

  The shape of the visual object. Can be one of the following: <box>, <cylinder>, <sphere>, <mesh>.

• material

  The color and texture of the link. The color is set of rgba numbers range from [0,1].

collision

The collision properties of a link. Simple collision models can reduce computation time. And also, multiple instances can exist.

• name: the name of collision model

Two subelements <origin> and <geometry> are same as above.

inertial

The link’s mass <mass>, positin of its center of mass <origin>, and its central inertia properties <inertia>.

joint

Describes the kinematics and dynamics of the joint.

• name
• type: can be one of the following:
  • revolute: rotates around the axis and has limits
  • continuous: rotates around the axis and has no limits
  • prismatic: sliding along the axis and has limits
  • fixed: no motions
  • floating: allows motions for 6 DoF
  • planar: allows motion in a plane perpendicular to the axis

parent

Parent link which can be defined by using link attribute.

child

Child link which also be defined by using link attribute.

axis

The joint axis normalized vector xyz specified for type of motion. Notice that floating and fixed do not use this field.

limit

The upper upper and lower motion limit for joint. Omit if joint is continous.

origin

The offset of position xyz and radians rpy.