Impedance Controller for Franka Emika Robots

This repository contains a ROS 2 Cartesian Impedance Controller specifically designed for Franka Emika research robots (fer, fr3, fp3). It utilizes franka_ros2 and franka_semantic_components to provide compliant motion control by adjusting robot joint torques based on a desired Cartesian pose.

General Function

The impedance_controller implements a virtual spring-damper system at the robot's end-effector.

• Compliant Control: Instead of moving rigidly to a point, the robot behaves like a mass attached to springs. If it encounters an obstacle, it will "give way" based on its defined stiffness.
• Dynamic Updating: The controller continuously calculates the necessary joint torques to maintain a target pose while compensating for Coriolis forces.
• Configuration: It reads translational and rotational stiffness parameters from a YAML configuration file to define how "stiff" or "soft" the robot behaves in Cartesian space.

Services

The package provides a custom service to dynamically update the robot's target pose without restarting the controller.

set_pose Service

• Purpose: This service allows an external node or user to update the desired Cartesian target (position and orientation) of the robot in real-time.

• Service Type: franka_msgs/srv/SetPose.

• Request Parameters:

• x, y, z: Target Cartesian position.

• roll, pitch, yaw: Target orientation in Euler angles.

• Behavior: When a request is received, the PoseInputServer (running on a dedicated thread within the controller) updates the target vectors used in the torque calculation loop.

How to Use

1. Launching the Controller

Use the provided launch file to start the robot bringup and the impedance controller:

ros2 launch impedance_controller impedance_controller.launch.py robot_ip:=<ROBOT_IP> arm_id:=fr3

• Key Arguments:
• robot_ip: The IP address of your Franka Control Unit.
• arm_id: The type of arm (default is fr3; supported: fer, fr3, fp3).
• load_gripper: Set to true if a Franka Gripper is attached.

2. Configuring Stiffness

Stiffness values can be adjusted in launch/controllers.yaml:

• translational_stiffness: Default is 150.0.
• rotational_stiffness: Default is 10.0.

3. Calling the Service

To move the robot to a new target pose via the command line:

ros2 service call /set_pose franka_msgs/srv/SetPose "{x: 0.5, y: 0.1, z: 0.4, roll: 3.14, pitch: 0.0, yaw: 0.0}"

Alternatively, you can run the included client node to send a hardcoded test pose:

ros2 run impedance_controller set_pose_client

License

This project is licensed under the Apache License 2.0.