Schunk EGU/EGK Gripper

This is the ROS2 driver for the SCHUNK EGU and EGK grippers. The driver communicates via the AnybusCom 40 interface and is compatible with grippers featuring PROFINET, Ethernet/IP, and EtherCAT. The driver currently supports most gripper functionalities, except for the jog mode.

System dependencies

We use the curl library for the HTTP-based communication to the devices. Install that system-wide with

sudo apt install curl libcurl4-openssl-dev

Build and install

Switch to the src folder of your current ROS2 workspace and

git clone https://github.com/SCHUNK-SE-Co-KG/schunk_egu_egk_gripper.git
sudo apt update -qq
rosdep update
rosdep install --from-paths ./ --ignore-src -y
cd ..
colcon build --symlink-install --packages-select schunk_egu_egk_gripper_driver schunk_egu_egk_gripper_library schunk_egu_egk_gripper_interfaces

Getting started

First, you'll need the IP address of your EGU/EGK gripper. The grippers should ship with DHCP by default. Let's say your own IP address is 192.168.0.3. You can then scan your local network to find the device with

nmap -sP -A 192.168.0.1/24

Let's say you obtained the 192.168.0.4 for the gripper. Now launch the driver with

source install/setup.bash
ros2 launch schunk_egu_egk_gripper_driver schunk.launch.py IP:=192.168.0.4

and you should be able to interact with the gripper.

You can adjust additional parameters in the driver's schunk.launch.py file, such as the frequencies of the joint_states or the state topics.

topic	parameter frequency
state	state_frq (1.0 Hz - ca. 60 Hz)
joint_states	rate

Note: The state topic will always publish the fastest rate. All other topics publish either at a slower rate or at the same rate, even if a faster rate is specified in the launch file. Actions always publish at the same rate as the state.

Note: There is also a namespace. It is recommended to set the model name as the namespace when using a single gripper. If you use multiple grippers of the same model, you can also utilize different namespaces.

Alternative Start

The provided driver functions as a component. This implies that you can initiate the Node in the following ways:

a) Using a component manager – this process is also outlined in the launch file.

b) Within your custom executable, coupled with a (multithreaded-)executor.

If you prefer starting the node in your main function, ensure that you include Schunk::schunk_egu_egk_gripper_driver in CMake's target_link_libraries(). Additionally, always specify the IP address, setting the parameter overrides "IP" to your designated IP.

Actions

All functionalities of the gripper, including movement, are treated as actions. This implies that when gripping, moving, or releasing a workpiece, you need to send a goal and can receive a result or feedback. Releasing a workpiece is the only action where you send an empty goal:

• move_to_absolute_position
• move_to_relative_position
• grip
• grip_with_position
• release_workpiece
• gripper_control

In contrast to the ROS1 driver, the gripping actions in ROS 2 always have the same name (grip and grip_with_pos). The ROS 2 driver still automatically recognizes the model and sets the appropriate goal based on the model.

'gripper_control' is the only action utilizing „control_msgs/action/GripperCommand“. It can be used for absolute movement (at half the maximal velocity) and gripping with or without a position. Please note that this action only supports external gripping.

Services

Services are functionalities that do not involve movement or occur so rapidly that feedback is unnecessary. If you require more information about the gripper during such operations, it is recommended to utilize the state topic.

• acknowledge
• stop
• fast_stop
• softreset
• parameter_get
• parameter_set
• release_for_manual_movement
• prepare_for_shutdown

Important: During a soft reset, no topics will be published. This will last for approximately 7 seconds. Afterward, all publications resume, and you can modify parameters.

Important: If you use prepare_for_shutdown, you also need to shut down the gripper, which can be also done using a soft reset.

Important: To exit from release_for_manual_movement, you need to activate fast_stop and acknowledge.

All other services can be used whenever you like. (Note: Fast stop is an abort of movement, so it always provokes an error).

With parameter_get and parameter_set you can read and set all allowed Parameter of the gripper. For getting and setting you need always the parameter instance. After that

Parameters

You can change parameter of the Gripper using dynamic reconfigure. Following parameters are available for change:

• use_brk
• grp_pos_margin
• grp_prepos_delta
• zero_pos_ofs
• grp_prehold_time
• wp_release_delta
• wp_lost_dst

For this type of parameter, you have to include the namespace: "GripperParameter." Example: GripperParameter.use_brk

You have the option to change the default values in the schunk.launch.py file, which will be loaded when you start the node.

Optionally, you can perform some basic commands to the gripper via Parameter. In this case, we recommend trying out rqt and opening the parameter reconfigure monitor.

Dynamic reconfiguration

We recommend using rqt to explore the capabilities of the gripper-driver. It lets you view all topics, dynamic reconfigure parameters, and services. You can also publish messages on topics (such as action goals) or call services. First, launch your driver as explained in Getting started. Open a new terminal

source install/setup.bash
rqt

Note that rqt currently has limitations in getting message classes for action feedback and action goals.

Open:

• Plugins/Configuration/Dynamic Reconfigure: For changing parameters.
• Plugins/Services/Service Caller: For calling services.
• Plugins/Topic/Topic Monitor: For viewing all messages.