Subscribe the topic /robot/joint_states ,but i get l_gripper_l_finger_joint message.

How to reject the {'l_gripper_l_finger_joint'}, i use subscribe Block and the topic /robot/joint_states ,but i get l_gripper_l_finger_joint message.

The physical Baxter sends the gripper states separately on the same topic, so we have to reject it. Can you help me with it.

I use the receive function to read the joint states，the same thing happened again.

The messages returned at different times are as follows,which i don't want these messages.

jntState1 = receive(jointSub1)
jntState1 = 
  ROS JointState message with properties:

    MessageType: 'sensor_msgs/JointState'
         Header: [1×1 Header]
           Name: {'l_gripper_l_finger_joint'}
       Position: 0.020830000000000
       Velocity: 0
         Effort: 0

These messages are what i want.

jntState1 = receive(jointSub1)
jntState1 = 
  ROS JointState message with properties:

    MessageType: 'sensor_msgs/JointState'
         Header: [1×1 Header]
           Name: {17×1 cell}
       Position: [17×1 double]
       Velocity: [17×1 double]
         Effort: [17×1 double]

In the simulink the messages returned at different times are as follows:

1、

2、

Can someone help me.

Best wishes！

[Cam Salzberger]

Just to make sure I'm understanding your situation, can you clarify on these points:

1. What is the situation in which you are using these messages? I'd like to clarify why you are choosing to use receive, instead of the LatestMessage property, or a NewMessageFcn callback.
2. What action are you taking after "receiving" the message? Are you calling this in a loop?
3. To clarify, are you happy with how Simulink is working for you, or did you have a question there too? It wasn't totally clear to me from your question.

Also, I just wanted to let you know that one common design pattern is to use the IsNew output of the Subscribe block to enable an enabled subsytem, so action is only taken when something new is received. You probably just didn't have it since this was just for demonstration purposes, but I wanted to make sure you were aware.

-Cam

[snow John]

Dear Mr Cam !

First of all, I want to thank you for your kindness response !

And I want use these messages to design my feedback controller in simulink and control the

Baxter robot .So i need to know the position and velocity of the joints.Then I use subscribe

block and the topic /robot/joint_states to get the messages from my Baxter robot.

Generally speaking，there are three different formats on the /robot/joint_states channel right

now. Note that 1 and 17 both occur in the same session!

%Length 1:
%       Real Baxter
%       'r_gripper_l_finger_joint' or 'l_gripper_l_finger_joint'
%       Note: I have never seen a X_gripper_r_finger_joint message on the
%       real Baxter.  It's not needed for the electric grippers.
%  Length 17:
%       Real Baxter
%       'head_nod', 'head_pan', 'left_e0', 'left_e1', 'left_s0', 'left_s1',
%       'left_w0', 'left_w1', 'left_w2', 'right_e0', 'right_e1','right_s0',
%       'right_s1', 'right_w0', 'right_w1', 'right_w2', and 'torso_t0'
%  Length 19:
%       Simulated Baxter
%       'head_pan', 'l_gripper_l_finger_joint', 'l_gripper_r_finger_joint',
%       'left_e0', 'left_e1', 'left_s0', 'left_s1', 'left_w0', 'left_w1', 
%       'left_w2', 'r_gripper_l_finger_joint', 'r_gripper_r_finger_joint',
%       'right_e0', 'right_e1', 'right_s0', 'right_s1', 'right_w0', 
%       'right_w1', and 'right_w2'

The physical Baxter sends the gripper states separately on the /robot/joint_states topic at

different times .That is why i said need to reject the {'l_gripper_l_finger_joint'}...,and just

get the information of Length 17 .

So do you have a good idea?

I am grateful for any reply.

Best wishes.

Answer 1

[Cam Salzberger]

Well, I was hoping to get your overall workflow so that I could suggest something that would fit in with it. However, the simpliest solution is simply to check what you have received after you get the message, but before you react with it. For example, if you are using receive in a loop, you can do something like:

while keepMoving
    jntStateMsg = receive(jointSub1);
    if contains(jntStateMsg.Name, 'head_pan')
        % react to he message here
    end
    pause(0.2)
end

You could even check the message to see if it has each specific joint you are using right before you use it. A similar pattern would apply if you were using a NewMessageFcn callback to the subscriber instead of receive, and using the LatestMessage property in a loop would be similar to receive.

So, overall, my advice would be to check that the message applies to the joints before you use it. Hope that helps!

-Cam

[snow John]

I understand, I will try to solve this problem with your suggestion in simulink.

Thank you again for your kindness help.

-John