Joint Limits Interface

Overview

joint_limits_interface contains data structures for representing joint limits, methods for populating them from common formats such as URDF and the ROS parameter server, and methods for enforcing limits on different kinds of hardware interfaces.

The joint_limits_interface is not used by controllers themselves (it does not implement a HardwareInterface) but instead operates after the controllers have updated, in the write() method (or equivalent) of the robot abstraction. Enforcing limits will overwrite the commands set by the controllers, it does not operate on a separate raw data buffer.

There are two main elements involved in setting up a joint limits interface:

• Joint limits representation

  • JointLimits Position, velocity, acceleration, jerk and effort.
  • SoftJointLimits Soft position limits, k_p, k_v (as described here).
  • Loading from URDF There are convenience methods for loading joint limits information (position, velocity and effort), as well as soft joint limits information from the URDF.
  • Loading from ROS params There are convenience methods for loading joint limits from the ROS parameter server (position, velocity, acceleration, jerk and effort). Parameter specification is the same used in MoveIt, with the addition that we also parse jerk and effort limits.

• Joint limits interface

  • For effort-controlled joints, the soft-limits implementation from the PR2 has been ported.
  • For position-controlled joints, a modified version of the PR2 soft limits has been implemented.
  • For velocity-controlled joints, simple saturation based on acceleration and velocity limits has been implemented.

Examples

Please refer to the joint_limits_interface wiki page.