end_effector current position

[SUUHOLEE]

hello mhubii

I want to return the current position of the end effector while the robot is moving, and I found that I should use the tf_2ros package. I installed it using the command:

sudo apt-get install ros-humble-tf2-ros

After that, I wrote the following code to return the current position of the end effector:

import rclpy from rclpy.node import Node import tf2_ros import geometry_msgs.msg

class EndEffectorPositionSubscriber(Node): def init(self): super().init('end_effector_position_subscriber') self.tf_buffer = tf2_ros.Buffer() self.tf_listener = tf2_ros.TransformListener(self.tf_buffer, self)

    self.timer = self.create_timer(1.0, self.get_current_pose)

    # Getting the names of base_link and end_effector_link as defined in the URDF file
    self.base_link = "link_0"
    self.end_effector_link = "link_ee"

def get_current_pose(self):
    try:
        transform = self.tf_buffer.lookup_transform(
            self.base_link,  # Robot's base link
            self.end_effector_link,  # Robot's end effector link
            rclpy.time.Time())

        current_pose = transform.transform.translation
        self.get_logger().info("Current End Effector Position: x={}, y={}, z={}".format(
            current_pose.x,
            current_pose.y,
            current_pose.z))
    except (tf2_ros.LookupException, tf2_ros.ConnectivityException, tf2_ros.ExtrapolationException) as e:
        self.get_logger().error("Failed to lookup transform: %s" % str(e))

def main(args=None): rclpy.init(args=args) end_effector_position_subscriber = EndEffectorPositionSubscriber() rclpy.spin(end_effector_position_subscriber) end_effector_position_subscriber.destroy_node() rclpy.shutdown()

if name == 'main': main()

This is the code that I am running. I don't know why the code isn't being written all at once.

However, I am getting the following error codes: [ERROR] [1716293460.470951577] [end_effector_position_subscriber]: Failed to lookup transform: "link_0" passed to lookupTransform argument target_frame does not exist. [ERROR] [1716293535.857385495] [end_effector_position_subscriber]: Failed to lookup transform: "link_ee" passed to lookupTransform argument source_frame does not exist.

I used this method, but an error occurred. Do you know where the error might be occurring? :( Alternatively, is there any other simple way to determine the position of the end effector?

[mhubii]

thanks for sharing the issue. The frames in this package use a prefix.

Can you try lbr/link_0 and lbr/link_ee. This is useful when using multiple robots.

self.base_link = "lbr/link_0"
self.end_effector_link = "lbr/link_ee"

[SUUHOLEE]

[INFO] [1716297729.229468116] [end_effector_position_subscriber]: Current End Effector Position: x=0.38000290978713525, y=-0.3300021408934912, z=0.999988303215718

thank you. end_effector position is print very well :)

[mhubii]

awesome! The prefix changes with the robot_name from the launch file