KAIRO - Modular Snake-like Inspection Robot

The department Interactive Diagnosis and Service Systems (IDS) began the development of modular inspection robots more than 15 years ago. The snake-like KAIRO 3 (Karlsruhe Autonomous Inspection Robot) represents the most recent snake-like robot following in the footsteps of its predecessors KAIRO (1997), Makro (1999), MakroPLUS (2004) and KAIRO II (2008). It has been developed for inspection and maintenance tasks, especially in areas which are difficult to access or dangerous for humans. Such areas are, for example, pipelines or maintenance shafts with small openings, or hazardous environments. With its modular and flexible construction, KAIRO 3 is well suited for a wide range of applications. This includes tasks like searching for explosives, inspection of narrow support tunnels and, of course, search and rescue missions after disasters.

Modular Hardware Construction

The chain-type structure of KAIRO 3 was biologically inspired by inchworms or snakes. KAIRO 3 can be classified as a heterogeneous modular robot, because it consists of two fundamentally different types of modules: drive modules and joint modules. The drive modules are used for wheeled locomotion. They are equipped with two mounting interfaces for connecting the joint modules at opposite ends. Each joint module consists of three active joints which are arranged at a 45-degree angle relative to each other. These active joints are driven by special harmonic drive gears designed to pass sufficient power to the joints. All joint angles are measured with optical encoders giving both absolute and incremental values.



Biologically inspired locomotion

A typical configuration of KAIRO 3 consists of six drive modules which are interleaved with five joint modules. A single drive module weighs 4.5 kg and is 146 mm long. The corresponding values for the joint module are 4 kg and 184 mm. Hence, for the previously mentioned configuration we get an overall robot length of about 1.8 m and an overall weight of about 47 kg. Due to the many degrees of freedom (KAIRO 3 consists of 27 DOF) such a robot system is also called hyper-redundant. Furthermore, KAIRO 3 is classified as an active system because every single DOF is driven by a motor. All actuators and control units are integrated inside the modules in such a compact way that it is easily possible to add several sensors, or even to transport objects inside of the drive modules.

System Architecture and Adaptive Control

The hierarchical control software is implemented using the robotic framework MCA2 (Modular Controller Architecture) and consists of three main parts: Base Control, Motion Execution and Manoeuvre Control. On the lowest level, the decentralized Base Control is located in every module of the robot to control the motors and to read in sensor values. These low-level control algorithms run on a specialized hardware module which is called UCoM (Universal Controller Module). This custom-made circuit board consists of a DSP and an FPGA. In addition to the motor control it also has an integrated component for measuring motor currents. The communication between all UCoMs and the adaptive control is realized by a CAN BUS.

KAIRO 3 Adaptive Control Architecture

In contrast to the decentralized Base Control, the Adaptive Control is executed on a centralized control computer and transmits the coordinating control commands via CAN BUS to every module. Controlling the overall robot system, the Adaptive Control itself consists of Manoeuvre Control and Motion Execution which adapts to the varying amount of modules. The Motion Execution processes the sensor data input and calculates the desired joint angles using the overall robot kinematics. At the top level the Manoeuvre Control plans the motion of the robot using a virtual rail. There is an initial set of elementary manoeuvres defined to achieve basic movements like Normal Drive or Inspection with KAIRO 3. Furthermore, two biologically-inspired locomotion manoeuvres have been implemented, which are called Omega and Caterpillar Locomotion. Every manoeuvre is implemented as a collection of states inside a hierarchical finite state machine.

Contact Person

Dipl.-Inform. Lars Pfotzer

Wissenschaftlicher Mitarbeiter



Lars Pfotzer studierte von 2003 bis 2009 Informatik an der Universität Karlsruhe (TH). Die Schwerpunkte seines Studiums lagen in den Bereichen Embedded Systems und Robotik. Seine Diplomarbeit "Entwicklung einer Navigationsplanung zur Inspektion von komplexen Umgebungen mit einem sechsbeinigen Laufroboter" fertigte er am FZI Forschungszentrum Informatik an.

Auf Grund seines Interesses an biologisch motivierten Robotersystemen ist er seit April 2010 Wissenschaftlicher Mitarbeiter in der Abteilung Interaktive Diagnose- und Servicesysteme (IDS) am FZI.


Phone: +49 721 9654-230
Fax: +49 721 9654-231
E-Mail: pfotzer@dont-want-spam.fzi.de

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