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Behavior of JointTrajectoryActionController with a single goal

asked 2011-03-15 07:30:05 -0500

Advait Jain gravatar image

If I send the JointTrajectoryActionController a single goal using the SimpleActionClient with a velocity and acceleration of 0 each, will the commanded motor torques simply be like a PID controller with a fixed set point?

Will the r_arm_controller (which I am assuming is a JointTrajectoryActionController) start behaving like a JointPositionController in this case?


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answered 2011-03-15 07:58:30 -0500

updated 2011-03-15 08:05:00 -0500

The desired position trajectory will be a fifth-order polynomial, with start and end boundary conditions of 0 velocities and accelerations. Also called a "minimum jerk" movement in some communities.

If you omit accelerations, you'll get a cubic spline. If you also omit velocities, you get linear interpolation. This is some documentation I found about this:

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thanks a lot Mrinal, this was really useful!
Advait Jain gravatar image Advait Jain  ( 2011-03-15 08:23:25 -0500 )edit

answered 2012-04-22 10:58:18 -0500

Hence, JointTrajectoryActionController actually covers a set of JointPositionControllers by allowing us to specify not only the final joint positions but also the final joint velocities and accelerations even if joint trajectory includes a single goal -at that moment-.

This way, we can extend the usage of joint position controller when we have many joints to control and the preferred control scheme is position control -like in the case of a movement mimicking robot- by creating one single controller that manages many joints at the same time. This saves us creating a JointPositionController plugin for every single joint.

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Asked: 2011-03-15 07:30:05 -0500

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Last updated: Apr 22 '12