fix an inverse kinematics bug

[ChengzhiSONG6]

transform translation error to spatial frame

[simonleonard]

Why is the translation error not in the spatial frame to start with?

[ChengzhiSONG6]

The translation error is in the spatial frame, it’s the Js column here is the screw axis description, which is not the same as velocity mapping for joint velocity to end effector velocity. https://groups.google.com/forum/#!topic/research-kit-for-davinci/srs_NPBw-fU

[simonleonard]

I cannot answer the question (whether you are right or not) if you do not give the kinematic chain of the robot.

Otherwise it is very possible that a robot's first joint results in 0 spatial linear velocity in a given configuration.