2. Traclabs
  3. trac_ik



The ROS packages in this repository were created to provide an alternative Inverse Kinematics solver to the popular inverse Jacobian methods in KDL. Specifically, KDL's convergence algorithms are based on Newton's method, which does not work well in the presence of joint limits --- common for many robotic platforms. TRAC-IK concurrently runs two IK implementations. One is a simple extension to KDL's Newton-based convergence algorithm that detects and mitigates local minima due to joint limits by random jumps. The second is an SQP (Sequential Quadratic Programming) nonlinear optimization approach which uses quasi-Newton methods that better handle joint limits. By default, the IK search returns immediately when either of these algorithms converges to an answer. Secondary constraints of distance and manipulability are also provided in order to receive back the "best" IK solution.

This repo contains 4 ROS packages:

  • trac_ik is a metapackage with build and complete Changelog info.

  • trac_ik_examples contains examples on how to use the standalone TRAC-IK library.

  • trac_ik_lib, the TRAC-IK kinematics code, builds a .so library that can be used as a drop in replacement for KDL's IK functions for KDL chains. Details for use are in trac_ik_lib/README.md.

  • trac_ik_kinematics_plugin builds a MoveIt! plugin that can replace the default KDL plugin for MoveIt! with TRAC-IK for use in planning. Details for use are in trac_ik_kinematics_plugin/README.md. (Note prior to v1.1.2, the plugin was not thread safe.)

As of v1.4.5, this package is part of the ROS Kinetic binaries: sudo apt-get install ros-kinetic-trac-ik (or indigo or jade).

A detailed writeup on TRAC-IK can be found here:

Humanoids-2015 (reported results are from v1.0.0 of TRAC-IK, see below for newer results).

Some sample results are below:

Orocos' KDL (inverse Jacobian w/ joint limits), KDL-RR (our fixes to KDL joint limit handling), and TRAC-IK (our concurrent inverse Jacobian and non-linear optimization solver; Speed mode) are compared below.

IK success and average speed (for successful solves) as of TRAC-IK tag v1.4.1. All results are from 10,000 randomly generated, reachable joint configurations. Full 3D pose IK was requested at 1e-5 Cartesian error for x,y,z,roll,pitch,yaw with a maximum solve time of 5 ms. All IK queries are seeded from the chain's "nominal" pose midway between joint limits.

Note on success: Neither KDL nor TRAC-IK uses any mesh information to determine if valid IK solutions result in self-collisions. IK solutions deal with link distances and joint ranges, and remain agnostic about self-collisions due to volumes. Expected future enhancements to TRAC-IK that search for multiple solutions may also include the ability to throw out solutions that result in self collisions (provided the URDF has valid geometry information); however, this is currently not the behaviour of any generic IK solver examined to date.

Note on timings: The timings provided include both successful and unsuccessful runs. When an IK solution is not found, the numerical IK solver implementations will run for the full timeout requested, searching for an answer; thus for robot chains where KDL fails much of the time (e.g., Jaco-2), the KDL times are skewed towards the user requested timeout value (here 5 ms).

Chain DOFs Orocos' KDL solve rate Orocos' KDL Avg Time KDL-RR solve rate KDL-RR Avg Time TRAC-IK solve rate TRAC-IK Avg Time
Atlas 2013 arm 6 75.54% 1.35ms 97.13% 0.39ms 99.97% 0.33ms
Atlas 2015 arm 7 75.71% 1.50ms 93.13% 0.81ms 99.18% 0.48ms
Baxter arm 7 61.07% 2.21ms 89.52% 1.02ms 99.17% 0.60ms
Denso VS-068 6 27.92% 3.69ms 98.13% 0.42ms 99.78% 0.38ms
Fanuc M-430iA/2F 5 21.07% 3.99ms 88.34% 0.92ms 99.16% 0.58ms
Fetch arm 7 92.49% 0.73ms 93.82% 0.72ms 99.96% 0.44ms
Jaco2 6 26.23% 3.79ms 97.66% 0.58ms 99.51% 0.58ms
KUKA LBR iiwa 14 R820 7 37.71% 3.37ms 94.02% 0.73ms 99.63% 0.56ms
KUKA LWR 4+ 7 67.80% 1.88ms 95.40% 0.62ms 99.95% 0.38ms
PR2 arm 7 83.14% 1.37ms 86.96% 1.27ms 99.84% 0.59ms
NASA Robonaut2 'grasping leg' 7 61.27% 2.29ms 87.57% 1.10ms 99.31% 0.67ms
NASA Robonaut2 'leg' + waist + arm 15 97.99% 0.80ms 98.00% 0.84ms 99.86% 0.79ms
NASA Robonaut2 arm 7 86.28% 1.02ms 94.26% 0.73ms 99.25% 0.50ms
NASA Robosimian arm 7 61.74% 2.44ms 99.87% 0.36ms 99.93% 0.44ms
TRACLabs modular arm 7 79.11% 1.35ms 95.12% 0.63ms 99.80% 0.53ms
UR10 6 36.16% 3.29ms 88.05% 0.82ms 99.47% 0.49ms
UR5 6 35.88% 3.30ms 88.69% 0.78ms 99.55% 0.42ms
NASA Valkyrie arm 7 45.18% 3.01ms 90.05% 1.29ms 99.63% 0.61ms

Feel free to email Patrick if there is a robot chain that you would like to see added above.