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Meaning of parameters of control_msgs/JointControllerState.msg

asked 2019-05-13 04:15:11 -0600

smilels gravatar image

updated 2019-05-13 04:38:40 -0600

gvdhoorn gravatar image


Can everyone help me explain the meaning of following parameters in JointControllerState message?

float64 set_point
float64 process_value
float64 process_value_dot
float64 error
float64 time_step
float64 command

Thanks a lot.

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answered 2019-05-13 04:48:37 -0600

gvdhoorn gravatar image

updated 2019-05-13 08:24:13 -0600

As the name implies (JointControllerState) this message is/may be used to publish the (internal) state of a joint (pid) controller.

As to the fields:

float64 set_point

the current set point (ie: desired state).

float64 process_value

the current value of the process (ie: latest sensor measurement on the controlled value).

float64 process_value_dot

first time-derivative of the process value.

float64 error

Essentially process_value - set_point (for a regular PID implementation).

float64 time_step

time between two consecutive updates/execution of the control law (ie: delta-t).

float64 command

current output of the controller.

As an example: see the JointVelocityController in ros_control.

Finally: it might be nice to contribute some comments to the message definition file in ros-controls/control_msgs if you now understand what the purpose of these fields is.

That would help future readers and users of the message avoid questions such as the one you posted.

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Thank you. Your answer is pretty clear. I have applied a pull request for ros-controls/control_msgs.

smilels gravatar image smilels  ( 2019-05-13 21:15:31 -0600 )edit

re: PR: very nice. Thank you for that.

gvdhoorn gravatar image gvdhoorn  ( 2019-05-14 02:10:18 -0600 )edit

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Asked: 2019-05-13 04:14:10 -0600

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Last updated: May 13 '19