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Simple Grasping

This document covers the simple_grasping_node executable in the grasping_control package.

Purpose

simple_grasping_node is a small sequence runner that calls two existing action servers:

  • grasping_msgs/action/MoveToNamedPose for arm motion
  • control_msgs/action/GripperCommand for gripper open and close commands

It is intended for simple scripted grasp routines where the robot should step through a fixed ordered sequence instead of waiting for an external planner or grasp pipeline.

Default Sequence

The default sequence is:

pre_grasp -> workspace_center -> open -> grasp_pose -> close -> post_grasp

Internally this is configured as:

[[pose, pre_grasp], [pose, workspace_center], [gripper, open], [pose, grasp_pose], [gripper, close], [pose, post_grasp]]

Each step has two fields:

  • pose, <named_pose>: send a MoveToNamedPose goal
  • gripper, open|close: send a GripperCommand goal using the configured open or close parameters

Running the Node

Run the node directly with:

source install/setup.bash
ros2 run grasping_control simple_grasping_node

Run it through the shared launch file with:

source install/setup.bash
ros2 launch grasping_control simple_grasping.launch.py

Run it through the UR wrapper launch with:

source install/setup.bash
ros2 launch grasping_ur simple_grasping.launch.py

Sequence Parameter

The sequence is configured through one parameter named sequence.

Example:

source install/setup.bash
ros2 launch grasping_ur simple_grasping.launch.py \
	sequence:="[[pose, pre_grasp], [pose, workspace_center], [gripper, open], [pose, grasp_pose], [gripper, close], [pose, post_grasp]]"

You can reorder, remove, or replace steps. For example, to skip workspace_center:

source install/setup.bash
ros2 launch grasping_ur simple_grasping.launch.py \
	sequence:="[[pose, pre_grasp], [gripper, open], [pose, grasp_pose], [gripper, close], [pose, post_grasp]]"

The parser also accepts a simpler list form such as:

["pose:pre_grasp", "gripper:open", "pose:grasp_pose"]

Parameters

Action Names

  • arm_action_name: default /move_arm_to_named_pose
  • gripper_action_name: default /gripper_command

Sequence

  • sequence: ordered list of [kind, value] pairs

Gripper Settings

  • open_position: default 0.09
  • open_max_effort: default 0.0
  • close_position: default 0.0
  • close_max_effort: default 5.0

Timeouts

  • server_timeout_sec: default 10.0
  • result_timeout_sec: default 120.0

Failure Behavior

The node stops at the first failed step.

  • If a named pose is rejected or fails in MoveIt, the sequence aborts.
  • If the gripper command does not reach its target, the sequence aborts.
  • If either action server is unavailable, the sequence exits before sending commands.

This node does not retry failed steps or branch based on runtime conditions. It is a deterministic executor for one configured ordered sequence.