Control · SDKs
RSI 5.x·
KUKA.RobotSensorInterface (RSI) is an optional package for KUKA KR C4 and KR C5 controllers, licensed at ~EUR 3,000 per controller. RSI exposes a hard real-time UDP/XML interface with a guaranteed cycle latency of **4 ms (250 Hz) or 12 ms (~83 Hz)** depending on robot type and version. The XML message carries correction setpoints for all axes (joint position offsets / Cartesian offsets in the base frame) — an external computer (PC with Ethernet) modifies the trajectory that the controller executes.
Architecture: in a KRL program the user calls `RSI_CREATE`, `RSI_ON`, `RSI_OFF` — every cycle the robot sends an XML packet with its current state (`<Rob>...</Rob>`) to the external client's UDP port, and the client returns a response with corrections (`<Sen>...</Sen>`). There is no retransmission — a lost packet means an emergency stop. This enforces network determinism: a dedicated switch / direct Ethernet, no WiFi, a separate VLAN. RSI is not an 'SDK' in the classical sense — it is a **wire protocol** plus controller-side runtime plus very thin helper libraries (KUKA only ships the XML schema and KRL examples).
The most popular uses: ROS integration via the community project `kuka_experimental` (Robot Web Tools / ROS-Industrial) with the `kuka_rsi_hw_interface` driver for ros_control, force control with an external FTS sensor (ATI, Schunk), seam tracking in welding (laser cameras from Meta Vision, Servo-Robot), tool path correction in robot milling (KUKA.CNC + RSI). For new applications the alternatives are **KUKA.PLC mxAutomation** (drag-and-drop function blocks for PLCs) or **KUKA Sunrise.OS** (for LBR iiwa — Java-based and considerably newer than RSI).
An API Library is a software package that exposes programmatic interfaces for communicating with a device, service, or system. In robotics it typically forms a lightweight integration layer built on top of the manufacturer's official API or an open-source project, abstracting low-level protocol details and providing language-native bindings (Python, C++, Java, etc.).
Middleware is a software layer that mediates between applications, services, sensors, drivers, and execution layers. In robotics, middleware is typically responsible for inter-process communication, message passing, hardware abstraction, and module integration within a single system. The most widely used robotics middleware is ROS (Robot Operating System), which provides a publish-subscribe message bus, service calls, and a rich ecosystem of packages.
Robot Control denotes the role of software responsible for motion control, command execution, coordination of actuating elements and the direct operational logic of the robot.
Device Integration denotes the role of software responsible for communication, configuration, initialization and handling of specific devices, sensors, controllers or hardware components within a robotic system.
A family of official SDKs and APIs provided by robot manufacturers: Boston Dynamics (Spot SDK), ABB (RobotStudio), KUKA (RSI / KUKA Sunrise), Universal Robots (URCap / RTDE), Agility Robotics (Digit SDK), Apptronik (Apollo SDK).
Arc welding with seam tracking (Meta Vision and Servo-Robot Quanta laser cameras) in Volkswagen, Daimler Truck and Liebherr plants. Robotic milling (KUKA.CNC + RSI) in aerospace — Airbus (Bremen), Boeing (composite trimming). Force control in assembly applications (with FTS ATI Mini58/Omega) — gearbox assembly at BMW Regensburg. Experimental use for dual-arm coordination (KUKA Innovation Award 2018–2022).
github.com/ros-industrial/kuka_experimental ~430★, ~280 forks. Active ROS-Industrial Working Group EU. KUKA Customer Portal (xpert.kuka.com) with RSI documentation — requires a service account. ROS-Industrial Discord ~5k members (general, including RSI discussions).
The external client should run on PREEMPT_RT Linux or Xenomai for deterministic 4 ms latency. The RSI package costs ~EUR 3,000 per controller. Requires KSS (KUKA System Software) ≥ 8.3 for KR C4 or ≥ 1.x for KR C5.
License family: Proprietary – Commercial
Support for new telemetry formats, optional TLS-encrypted XML (for IT-network deployments).
Adapted for the KR C5 controller (new generation, smaller enclosure). Full backwards compatibility for KRL programs.
Better integration with KUKA.SafeOperation (SIL2/PLd safety categories), EtherCAT bridge support.
Adaptation for KR C4 (Linux/Windows hybrid), 4 ms cycle, improved XML schema.
First release for the KR C2 controller, 12 ms cycle.
