Place an object

Placing is the mirror image of picking, but with a different failure mode: releasing the object is the moment you lose control of it. A placement that lets go too early drops the object; one that descends too far jams it into the surface. This guide walks through a four-step placement that controls those two failure modes: move to a pre-place pose, descend to the placement surface, release, and retreat straight up so you do not disturb what you just set down.

Prerequisites

• Object already grasped (see Pick an object).
• Placement location known in world coordinates.

The code below continues from Pick an object; motion_service, gripper, and world_state are already defined in that script.

Steps

1. Move to pre-place position

# Pre-place: above the target location
pre_place = PoseInFrame(
    reference_frame="world",
    pose=Pose(
        x=500, y=0, z=200,
        o_x=0, o_y=0, o_z=-1, theta=0
    )
)

await motion_service.move(
    component_name="my-arm",
    destination=pre_place,
    world_state=world_state
)

2. Descend to the placement surface

The descent pose puts the object where you want it to end up. SURFACE_HEIGHT is the world-frame z of the placement surface plus half the object’s height (roughly: you want the bottom of the object touching the surface at release). For a known surface, measure once and hard-code it. For a detected surface, set it from the vision result.

# Place: at the surface.
# Set z to the height of the placement surface in your workspace.
# For example, if you detected the target location, use its z coordinate.
SURFACE_HEIGHT = 50  # mm: world-frame z of the surface plus half the object's height
place_pose = PoseInFrame(
    reference_frame="world",
    pose=Pose(
        x=500, y=0, z=SURFACE_HEIGHT,
        o_x=0, o_y=0, o_z=-1, theta=0
    )
)

await motion_service.move(
    component_name="my-arm",
    destination=place_pose,
    world_state=world_state
)

3. Release and retreat

# Open gripper to release
await gripper.open()
print("Object placed")

# Retreat: lift straight up
retreat_pose = PoseInFrame(
    reference_frame="world",
    pose=Pose(
        x=500, y=0, z=200,
        o_x=0, o_y=0, o_z=-1, theta=0
    )
)

await motion_service.move(
    component_name="my-arm",
    destination=retreat_pose,
    world_state=world_state
)
print("Retreated from placement")

Tips

• Keep the object level on the way down. A carried object with an open top (a cup, an open box) spills if the gripper tilts during descent. Add an OrientationConstraint, which locks the end effector’s tilt, with a tolerance of 3 to 5 degrees for the descent segment; remove it for the retreat.
• Retreat straight up. Any lateral motion during retreat can catch the object the gripper just released. Plan the retreat pose with the same x and y as the place pose and only the z raised.
• Update WorldState after release. The placed object is now a static obstacle. If the next motion passes near the placement location, add a Geometry matching the placed object to WorldState.obstacles so the planner routes around it.

What’s next

• Pick an object: the pick half of the pick-and-place workflow.