ServerFriRos2

ServerFriRos2 is a KUKA Sunrise Cabinet controller program that creates an FRI connection between the KUKA LBR iiwa and a ROS 2 computer. Through this connection, ros2_control receives the current robot state and, depending on the selected mode, sends motion commands to the controller.

The program connects the two parts of the system: the KUKA controller application and the ROS 2 control node on the external computer. A physical robot cannot be controlled through ROS 2 unless ServerFriRos2 is running.

The program has been tested on a KUKA LBR iiwa 7 R800 with Sunrise OS 1.16 and FRI 1.16. The source code is located at src/iiwa_sunrise/src/ServerFriRos2.java.

See FRI protocol for an overview of the communication channel and SunriseWorkbench setup for cabling and Sunrise project preparation.

Before starting

Verify that the configured initial positions are safe for the installed tool and robot cell. Keep the workspace clear during automatic motion. Impedance and manual-guidance modes do not replace standard KUKA safety functions.

Required configuration

Before synchronizing the project with the controller, open ServerFriRos2.java in Sunrise Workbench and check the parameters for your setup.

Network addresses

The Java class contains addresses of the ROS 2 computer as seen through each controller interface:

private static final String KONI_IP = "192.170.10.10";
private static final String KLI_IP  = "192.168.21.31";

Do not confuse these with robot.ip in cobot-setting.yaml. That parameter is the address of the KUKA controller accessed by the ROS 2 computer. See System configuration for details.

Tool and load data

The program attaches the tool named in the @Named annotation to the flange:

@Named("tool1")
private Tool _tool;

Replace tool1 with the tool name from Sunrise Workbench → Object Templates. In Monitor mode, Load Data must contain the mass, center of mass, and inertia tensor. Before enabling gravity compensation, the program checks these parameters and warns the operator if the load model is invalid.

See Load data for calibration and verification instructions.

Initial positions

Before FRI starts, the robot automatically moves to one of the configured joint positions:

private static final double[] ZERO_POSITION =
    {0, 0, 0, 0, 0, 0, 0};

private static final double[] MONITOR_WORKING_POSITION =
    {0, 0, 0, -1.57, 0, 1.57, 0};

ZERO_POSITION is used in Position and JointImpedance modes. In Monitor mode, the robot first passes through the zero position and then moves to MONITOR_WORKING_POSITION. If necessary, change these arrays to prevent collisions with fixtures, the table, or the installed tool.

FRI period

For Position and JointImpedance, the value selected on the smartPAD must match robot.fri_cycle_ms in cobot-setting.yaml:

Selected period	Update rate	When to use it
10 ms	100 Hz	Standard and most stable option; required for KLI
5 ms	200 Hz	Higher-rate control through the dedicated KONI interface

Monitor uses a fixed 2 ms period and does not display a separate period-selection dialog.

Starting the application

Open Applications on the smartPAD, find ServerFriRos2 in the robot application list, and activate it. The program then appears in the top smartHMI bar.

Press the green Start button on the smartPAD. The program prompts you to select a network interface, control mode, and any additional FRI parameters required by that mode.

Step 1: selecting the network interface

The first dialog displays the configured ROS 2 computer addresses. Select the interface to which the control computer is physically connected.

Interface	Characteristics	Available modes	Period
KONI (X66)	Dedicated FRI network; recommended	Position, JointImpedance, Monitor	5 or 10 ms; Monitor: 2 ms
KLI (X6)	Shared control network; fallback option	Position, JointImpedance	10 ms only

KONI is better suited to real-time control because its dedicated channel provides lower latency and a more stable cycle. Use KLI when KONI is unavailable. Monitor mode is disabled over KLI because of shared-network latency.

Step 2: selecting the control mode

Available buttons depend on the selected network interface.

Over KLI, only Position and JointImpedance are available:

Over KONI, Monitor is also available:

Position

Position is the primary mode for ordinary ROS 2 control, including MoveIt trajectory execution. The controller follows position commands precisely; joint stiffness cannot be adjusted in this mode.

After the parameters are selected, the robot moves to ZERO_POSITION, creates an FRI session in POSITION command mode, and waits for the ROS 2 client.

JointImpedance

JointImpedance also receives position commands from ROS 2, but executes them with configured joint stiffness. Use this mode to control mechanical impedance while following a target trajectory.

After selecting the mode, the program asks for one stiffness value for all seven joints:

Stiffness	Robot behavior
1500 Nm/rad	Stiffest command tracking among the available options
1000 Nm/rad	High joint stiffness
800 Nm/rad	Medium joint stiffness
500 Nm/rad	Softest behavior among the available options

The program sets damping to 0.7 for every joint. After configuration, the robot moves to ZERO_POSITION and waits for an FRI client as in Position mode.

Monitor

Monitor is intended for manual guidance while transmitting the current robot state to ROS 2. The computer sends no motion commands: the FRI session uses NO_COMMAND_MODE, and the controller transmits joint positions and torques every 2 ms.

Before connecting, the robot moves through ZERO_POSITION to MONITOR_WORKING_POSITION. The program then checks the tool Load Data and enables joint impedance with zero stiffness and damping of 0.7. Gravity compensation allows the robot to be guided carefully by hand.

Start the ROS 2 node on the computer before confirming the dialog. Press OK — ROS2 ready only after ros2_control_node is active.

Monitor and the load model

Do not enable manual guidance with invalid tool parameters. Incorrect mass, center of mass, or inertia makes gravity compensation inaccurate: the robot may resist the operator or drift unexpectedly.

Step 3: selecting the send period

For Position or JointImpedance over KONI, the program offers a 10 or 5 ms period. Over KLI, this step is skipped because the period is fixed at 10 ms.

Start with 10 ms unless the task requires a higher control rate. Use 5 ms over KONI only for tasks that need a 200 Hz cycle.

Connecting ROS 2

Start the physical-robot stack on the ROS 2 computer:

cobot run

Select the physical robot when prompted. The command starts ros2_control_node, the FRI hardware interface, controllers, MoveIt, and configured additional services. See cobot CLI commands and Control via ROS 2.

For the most reliable startup, run cobot run on the computer first and then start ServerFriRos2 on the smartPAD. If the KUKA application is already waiting for a client, ROS 2 must start within 30 seconds. After the timeout, the program closes the FRI session and reports an error in the log.

After connection, the smartHMI log displays:

• FRI session state;
• connection quality;
• latency;
• packet delivery time variation (jitter).

When the FRI client stops, the session closes, the active mode ends, and connection resources are released. Start the smartPAD application again for a new connection.

If the connection cannot be established

Check the following first:

1. The selected interface is the one connected to the ROS 2 computer.
2. KONI_IP or KLI_IP matches the computer address on the selected network.
3. cobot-setting.yaml contains the KUKA controller address, not the computer address.
4. The 5/10 ms period in the Java program matches robot.fri_cycle_ms.
5. ros2_control_node starts before the 30-second timeout expires.
6. FRI UDP port 30200 is configured and not blocked by a firewall.

If the application cannot start because the tool or frame configuration was lost, see Configuration error.