[ros-users] Introducing A Better Inverse Kinematics Package

[Patrick Beeson]

Andreas,

My experience with openrave kinematics has been with ikfast.  Ikfast first runs offline on a model to create a "closed form" IK solution.  This really only works with 6-DOF and lower chains.  Additionally, I've found that ikfast solutions are generally not very precise,  including providing answers near but still slightly outside joint limits and providing joint configuration answers that when pushed back through the forward kinematics are not very close to the original desired Cartesian pose.  Thus, in the past when I've used ikfast, I also end up having to run KDL (or trac-IK) afterwards to quickly coverage to a solution with small (< 1e-2) residual error wrt the desired Cartesian pose.  Finally ikfast does not allow tolerances for Cartesian dimensions, which allows things like position only solutions or for example solutions where end effector roll can fall within a range.


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> On Nov 5, 2015, at 3:47 PM, andreas.tenpas--- via ros-users <ros-users at lists.ros.org> wrote:
> 
> This is neat! Thanks for sharing!
> 
> I would be interested in how this performs in comparison to openrave.
> 
> Best,
> 
> Andreas
> 
> 
> -------- Original Message --------
> Subject: [ros-users] Introducing A Better Inverse Kinematics Package
> From: Patrick Beeson via ros-users 
> To: ros-users at lists.ros.org
> CC: 
> 
> 
> TRACLabs Inc. is glad to announce the public release of our Inverse Kinematics solver TRAC-IK.  TRAC-IK is a faster, significantly more reliable drop-in replacement for KDL's pseudoinverse Jacobian solver.
> 
> Source (including a MoveIt! plugin) can be found at:
> https://bitbucket.org/traclabs/trac_ik.git
> 
> TRAC-IK has a very similar API to KDL's IK solver calls, except that the user passes a maximum time instead of a maximum number of search iterations.  Additionally, TRAC-IK allows for error tolerances to be set independently for each Cartesian dimension (x,y,z,roll,pitch.yaw).
> 
> More details:
> 
> KDL's joint-limited pseudoinverse Jacobian implementation is the solver used by various ROS packages and MoveIt! for generic manipulation chains.  In our research with Atlas humanoids in the DARPA Robotics Challenge and with NASA's Robotnaut-2 and Valkyrie humanoids, TRACLabs researchers experienced a high amount of solve errors when using KDL's inverse kinematics functions on robotic arms.  We tracked the issues down to the fact that theoretically-sound Newton methods fail in the face of joint limits.  As such, we have created TRAC-IK that concurrently runs two different IK methods: 1) an enhancment of KDL's solver (which detects and mitigates local minima that can occur when joint limits are encountered during gradient descent) and 2) a Sequential Quadratic Programming IK formulation that uses quasi-Newton methods that are known to better handle non-smooth search spaces.  The results have been very positive.  By combing the two approaches together, TRAC-IK outperforms both standalone IK methods with no additional overhead in runtime for small chains, and significant improvements in time for large chains.
> 
> Details can be found here in our Humanoids 2015 paper here:
> https://personal.traclabs.com/~pbeeson/publications/b2hd-Beeson-humanoids-15.html
> 
> A few high-level results are shown in the attached (low-res) figure.
> 
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