Control Gripper using Python

[baberjunaid]

Dear all,

I am learning and find it difficult from the doc to get real understanding to control the Franka using Python and ROS.

following terminal command close the gripper

rostopic pub /franka_gripper/move/goal franka_gripper/MoveActionGoal "header:
  seq: 0
  stamp:
    secs: 0
    nsecs: 0
  frame_id: ''
goal_id:
  stamp:
    secs: 0
    nsecs: 0
  id: ''
goal:
  width: 0.0
  speed: 1.0" 

Now if I want to do similar thing using python. I have written following code in a package

import rospy
from std_msgs.msg import String
import franka_gripper.msg

def my_listener():
    pub = rospy.Publisher('/franka_gripper/move/goal', franka_gripper.msg.MoveActionGoal, queue_size=10)
    rospy.init_node('my_listener', anonymous=True)
    rate = rospy.Rate(10) # 10hz
    while not rospy.is_shutdown():
	goal = franka_gripper.msg.MoveGoal(width=0.5, speed=1.0)
        #hello_str = "hello world %s" % rospy.get_time()
        #rospy.loginfo('Publishing')
        pub.publish(goal)
        rate.sleep()

if __name__ == '__main__':
    try:
        my_listener()
    except rospy.ROSInterruptException:
        pass

but I get following error

 rosrun my_gripper my_listener.py 
Traceback (most recent call last):
  File "/home/panda/ros_catkin/src/my_gripper/scripts/my_listener.py", line 56, in <module>
    my_listener()
  File "/home/panda/ros_catkin/src/my_gripper/scripts/my_listener.py", line 51, in my_listener
    pub.publish(goal)
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rospy/topics.py", line 879, in publish
    data = args_kwds_to_message(self.data_class, args, kwds)
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rospy/msg.py", line 121, in args_kwds_to_message
    raise TypeError("expected [%s] but got [%s]"%(data_class._slot_types[0], arg._type))
TypeError: expected [std_msgs/Header] but got [franka_gripper/MoveGoal]

[marcbone]

The movement of the gripper is an action. While it should be possible to make it work with a publisher, you should consider making it an action client. You can read about them here

You can also take my comment in #256 as a starting point

[baberjunaid]

Dear marcbone,

Thank you. I changed the code as following by going through your starting point;

import franka_gripper.msg
import rospy
import sys

# Brings in the SimpleActionClient
import actionlib


# Brings in the messages used by the grasp action, including the
# goal message and the result message.

def move_gripper():
    # Creates the SimpleActionClient, passing the type of the action
    client = actionlib.SimpleActionClient('/franka_gripper/move/goal', franka_gripper.msg.MoveActionGoal)

    # Waits until the action server has started up and started
    # listening for goals.
    client.wait_for_server()

    # Creates a goal to send to the action server.
    goal = franka_gripper.msg.MoveActionGoal()
    goal.width = 0.022
    goal.speed = 1.0
    
    # Sends the goal to the action server.
    client.send_goal(goal)

    # Waits for the server to finish performing the action.
    client.wait_for_result()

    # Prints out the result of executing the action
    return client.get_result()  # A GraspResult


if __name__ == '__main__':
    try:
        # Initializes a rospy node so that the SimpleActionClient can
        # publish and subscribe over ROS.
        rospy.init_node('junaid_gripper')
        result = move_gripper()
        print("Success: ",result.success)
        print("Error message: ", result.error)
    except rospy.ROSInterruptException:
        print("program interrupted before completion", file=sys.stderr)

It still not working. Secondly, why my mouse cursor changes and i get control back of mouse only if kill the process. Kindly help.

[baberjunaid]

I figured out my mistake. Thank you. Here is the solution for the community. You may close the issue.

import franka_gripper.msg
import rospy
import sys

# Brings in the SimpleActionClient
import actionlib


# Brings in the messages used by the action, including the
# goal message and the result message.

def move_gripper():
    
    # Creates the SimpleActionClient, passing the type of the action
    client = actionlib.SimpleActionClient('/franka_gripper/move', franka_gripper.msg.MoveAction)

    # Waits until the action server has started up and started
    # listening for goals.
    client.wait_for_server()

    # Creates a goal to send to the action server.
    goal = franka_gripper.msg.MoveGoal(width=0.001, speed=1.0)
    #goal.width = 0.022
    #goal.speed = 1.0
    
    # Sends the goal to the action server.
    client.send_goal(goal)

    # Waits for the server to finish performing the action.
    client.wait_for_result()

    # Prints out the result of executing the action
    return client.get_result()  # A move result


if __name__ == '__main__':
    try:
        # Initializes a rospy node so that the SimpleActionClient can
        # publish and subscribe over ROS.
        rospy.init_node('junaid_gripper')
        result = move_gripper()
        print("Success: ",result.success)
        print("Error message: ", result.error)
    except rospy.ROSInterruptException:
        print("program interrupted before completion")