urdf备忘

urdf的规范，可以在这里查
http://wiki.ros.org/urdf/XML

joint
type (required)

Specifies the type of joint, where type can be one of the following:
1revolute - a hinge joint that rotates along the axis and has a limited range specified by the upper and lower limits.
2continuous - a continuous hinge joint that rotates around the axis and has no upper and lower limits
3prismatic - a sliding joint that slides along the axis, and has a limited range specified by the upper and lower limits.
4fixed - This is not really a joint because it cannot move. All degrees of freedom are locked. This type of joint does not require the axis, calibration, dynamics, limits or safety_controller.
5floating - This joint allows motion for all 6 degrees of freedom.
planar - This joint allows motion in a plane perpendicular to the axis.