rerail_stretchit_manipulation

This package was designed for and tested with a Stretch 2 Mobile Manipulator from Hello Robot.

Package Description

This package's primary component is manipulation_grasp.py, a ROS Noetic service utilized by the behavior tree of the stretch stack. It operates with a custom message defined in RerailManip.srv located in the srv folder. The service accepts a geometry_msgs/Pose target_pose as input and returns a Boolean message upon completing the manipulation task. The manipulation process employs the StretchIK class from src/manipulation/ik.py. This class computes the inverse kinematics for the provided pose message to derive the joint values necessary to reach the targeted object. This script is inspired by Hello Robot's Inverse Kinematics Tutorial Workshop and a previous implementation by mlamsey.

Other Important Files:

• manipulation_delivery.py: A service for executing predefined trajectories to place a grasped object on a surface, returning a Boolean message.
• move_camera: A service for repositioning the robot's camera to a predefined location, enhancing object visibility for grasping.
• urdf_ripper.py: Adapted from mlamsey's stretch_ik repository, this script streamlines the robot's original URDF file by eliminating unnecessary links, generating a new, optimized version.

Inputs and Outputs (ROS msg types)

• manipulation_grasp.py:
  • Input: geometry_msgs/Pose / Output: std_msgs/Bool.msg
• manipulation_delivery.py:
  • Input: None / Output: std_msgs/Bool.msg
• move_camera:
  • Input: None / Output: std_msgs/Bool.msg

Generating a URDF for ikpy

The /urdf folder contains a simplified URDF file for ikpy usage. To regenerate it (for instance, after calibrating your Stretch URDF), follow these instructions:

1. Navigate to /src using cd.
2. Run python urdf_ripper.py --save_path /path/to/output/urdf/stretch.urdf.
3. Move the generated URDF file to /urdf and ensure it is named stretch.urdf.

The urdf_ripper.py script discards all extraneous links and joints from the original URDF and saves the streamlined version to the specified output path. The script is based on a tutorial notebook.

Robot Coordinate System

For ease of inverse kinematics calculations, the robot is treated as a Cartesian manipulator. Here, the x-axis represents base translation, the y-axis denotes arm extension, and the z-axis signifies the height of the robot's arm. The robot must always be perpendicular to the surface from which it intends to grasp objects.

Tips

Review the hardcoded values in manipulation_grasp.py and manipulation_delivery.py. While these values are generally effective for most surfaces, it's crucial to test them in your specific setup to prevent potential collisions.

Dependencies

This package depends on ikpy. You can install it using the following command:

pip3 install -q ikpy