Planning scene and collision objects

Note

The following examples use the ROS backend and the MoveI! planner for UR5 robots. Before running them, please make sure you have the ROS backend correctly configured and the UR5 Demo started.

To plan motion paths that avoid collisions with other objects than the robot itself, the backend’s planning scene has to be updated.

This is the representation of the planning scene in RViz with the UR5.

../../_images/05_collision_objects_attached_without.jpg

Note

If using Docker to run ROS, you can open RViz on your browser.

Collision meshes

The following script adds and then removes a floor to the planning scene.

import time

from compas.datastructures import Mesh

import compas_fab
from compas_fab.backends import RosClient
from compas_fab.robots import CollisionMesh
from compas_fab.robots import PlanningScene

with RosClient() as client:
    robot = client.load_robot()
    scene = PlanningScene(robot)
    assert robot.name == 'ur5_robot'

    mesh = Mesh.from_stl(compas_fab.get('planning_scene/floor.stl'))
    cm = CollisionMesh(mesh, 'floor')
    scene.add_collision_mesh(cm)

    # sleep a bit before removing the floor
    time.sleep(1)

    scene.remove_collision_mesh('floor')

The backend’s updated planning scene while executing the above script.

../../_images/05_collision_objects.jpg

The following script adds several boxes (bricks) to the planning scene. Here, we use append instead of add to have multiple collision objects clustered under the same identifier. Like that, we don’t need to keep track of all identifiers when we later remove them.

import time

from compas.datastructures import Mesh
from compas.geometry import Box

from compas_fab.backends import RosClient
from compas_fab.robots import CollisionMesh
from compas_fab.robots import PlanningScene

with RosClient() as client:
    robot = client.load_robot()
    scene = PlanningScene(robot)
    assert robot.name == 'ur5_robot'

    brick = Box.from_width_height_depth(0.11, 0.07, 0.25)

    for i in range(5):
        mesh = Mesh.from_vertices_and_faces(brick.vertices, brick.faces)
        cm = CollisionMesh(mesh, 'brick')
        cm.frame.point.y += 0.5
        cm.frame.point.z += brick.zsize * i

        scene.append_collision_mesh(cm)

    # sleep a bit before removing the bricks
    time.sleep(1)

    scene.remove_collision_mesh('brick')

The backend’s updated planning scene while executing the above script. Note the red robot link indicating the collision.

../../_images/05_collision_objects_append.jpg

Attach tool to a robot’s end-effector

The following script defines a tool, described by a collision mesh and a frame, and attaches and removes it to the robot’s end-effector.

import time

from compas.datastructures import Mesh
from compas.geometry import Frame

import compas_fab
from compas_fab.backends import RosClient
from compas_fab.robots import PlanningScene
from compas_fab.robots import Tool

with RosClient() as client:
    robot = client.load_robot()
    scene = PlanningScene(robot)
    assert robot.name == 'ur5_robot'

    # create collision object
    mesh = Mesh.from_stl(compas_fab.get('planning_scene/cone.stl'))
    t1cf = Frame([0.14, 0, 0], [0, 0, 1], [0, 1, 0])          # TODO: check this frame!
    tool = Tool(mesh, t1cf, name='tip')
    scene.add_attached_tool(tool)

    # sleep a bit before removing the tip
    time.sleep(1)

    # check if it's really there
    planning_scene = robot.client.get_planning_scene()
    acm = planning_scene.robot_state.attached_collision_objects
    assert acm[0].object['id'].startswith('tip_')

    scene.remove_attached_tool()

    planning_scene = robot.client.get_planning_scene()
    assert acm[0].object['id'] not in [c.object['id'] for c in planning_scene.robot_state.attached_collision_objects]

The backend’s updated planning scene while executing the above script.

../../_images/05_collision_objects_attached.jpg