Ask Your Question
1

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?

Thanks.

edit retag flag offensive close merge delete

2 Answers

Sort by ยป oldest newest most voted
3

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: http://www.ros.org/wiki/robot_mechanism_controllers/JointSplineTrajectoryController

edit flag offensive delete link more

Comments

thanks a lot Mrinal, this was really useful!
Advait Jain gravatar image Advait Jain  ( 2011-03-15 08:23:25 -0500 )edit
0

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.

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Question Tools

1 follower

Stats

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

Seen: 442 times

Last updated: Apr 22 '12