Intelligent Structures for Mobile Robots

The four-legged robot in DFKI's artificial crater environment (Source: Daniel Kühn, DFKI GmbH)
The four-legged robot in DFKI's artificial crater environment (Source: Daniel Kühn, DFKI GmbH)
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The aim of the project iStruct is to develop a robotic system as well as biologically inspired structural components which, if applied on the robotic system, effectively improve the locomotion and mobility characteristics. In order to achieve this goal, an improved perception of the environment and the own condition is needed. The structures designed and build are as self-contained as possible with regard to sensing, sensor preprocessing, control and communication. The biologically inspired robot itself is an ideal test platform for the foot and spine structures. These structures can extend the already existing locomotion behaviors of a robot and are used contemporaneous as carrier and sensor system. This way, different functionalities are united in one construction unit.

Duration: 15.05.2010 till 15.08.2013
Donee: German Research Center for Artificial Intelligence GmbH & University of Bremen
Sponsor: Federal Ministry of Economics and Technology
German Aerospace Center e.V.
Grant number: This project is funded by the Space Agency of the German Aerospace Center with federal funds of the Federal Ministry of Economics and Technology (BMWi) in accordance with the parliamentary resolution of the German Parliament, grant no. 50RA1013 (DFKI) and 50RA1014 (University of Bremen).
Partner: University of Bremen
Application Field: Space Robotics
Related Projects: SpaceClimber
A Semi-Autonomous Free-Climbing Robot for the Exploration of Crater Walls and Bottoms (07.2007- 11.2010)
(07.2008- 12.2009)
Related Software: MARS
Machina Arte Robotum Simulans
Node Level Data Link Communication

Project details

Spinal column concept equipped with BLDC motors (Source: Daniel Kühn, DFKI GmbH)
The iStruct Demonstrator (Source: Frank Beinersdorf, DFKI GmbH)
Bioinspired functionality - Developmental steps of the lower leg design (Source: Felix Bernhard und Kristin Fondahl, DFKI GmbH)

The focus of this project lies on the design of a robot demonstrator and the development of intelligent structures for application in mobile robot systems, especially in walking machines. Project goal is to increase the efficiency of a complex walking robot by using intelligent structures. In order to achieve this goal, rigid or connecting elements are extended to single subsystems. These subsystems provide an advantage to the overall system in which they are used by delivering enhanced mobility and sensor information. For testing and evaluation of the intelligent structures, a suitable robot demonstrator will be developed.

To increase the mobility towards a so-called multi-locomotion system (i.e. providing the means to walk quadrupedally or bipedally), the rigid connection between the front and rear body will be replaced by an actuated spinal column (see Figure 1). This active artificial spine effectively improves the locomotion and mobility capabilities when applied to a mobile robotic system.

The natural spinal column is not an independent functional unit, but must be considered as subcomponent of a more complex biomechanical system consisting of a variety of muscles, bones and tendons. To replicate this functionality a parallel kinematic is used. A parallel kinematic has excellent properties for body structures of mobile robots, as in some motions sequences like fast walking, high inertial forces appear and a stiff structure is beneficial. Furthermore, the load in such a structure is shared and multiple actuators are involved in generating motions. Each of the six drive chain of the torso section is actuated by a brushless DC motor (BLDC) with a high reduction ratio gear (Figure 2). To determine the motor states, optical incremental encoders and absolute magnetic encoders are added to the mounting.

Another step towards allowing bipedal walking is the development of more advanced hind feet (Figure 3). Most multi-legged robots are equipped with single-point-contact feet for the sake of simplicity in design and control. Still, multi-point-contact feet (MPCF) can improve traction control in quadrupedal walking and allow bipedal walking. To make use of these advantages the lower legs of the robotic system were developed and integrated with an actuated ankle joint, an attached MPCF-structure and a set of sensors with their required electronics. The lower leg structure is actively and passively adaptable with three passive DOF near the ankle, two active DOF in the ankle and two active DOF in the toe joints. To control this high level of adaptability the feet have a very high sensor density including among others a 6-axis force/torque sensor, a pressure sensor array of 43 FSR-sensors, a digital 3-axis accelerometer and digital magnetic angular encoders to monitor every moving axes of the foot and ankle structure. A custom circuit board was developed to process the sensor data locally and to limit data traffic on the robot. Thus the foot including its electronics provides a self-contained unit.


iStruct: Stand-up motion

In dem Video ist eine Transition von der vierbeinigen Grundhaltung in den bipedalen Stand zu sehen. Der dank der künstlichen Wirbelsäule neu gewonnene Bewegungsfreiraum wird aufgezeigt, während der Roboter Charlie auf zwei Beinen steht.

iStruct: Walking

Das Video zeigt den iStruct Demonstrator beim Laufen. Neben verschiedenen Laufrichtungen wurden auch fließende Bewegungen zwischen den jeweiligen Richtungen realisiert.

iStruct: Balancing

Der Roboter verschiebt seinen Schwerpunkt basierend auf der Schräglage, in der er sich befindet.

More Images

Der innerhalb des Projekts iStruct entwickelte Roboter mit beweglicher Wirbelsäule und Sensorfuß (seitliche Ansicht) (Foto: Daniel Kühn, DFKI GmbH)
Lateral view on the developed ape-like robot with arti cial spine and sensor feet (Photo: Daniel Kühn, DFKI GmbH)
Detailaufnahme der Fußaktuierung (Foto: Daniel Kühn, DFKI GmbH)
Close up picture of the ankle joint mechanism and sensor foot (Photo: Daniel Kühn, DFKI GmbH)
Detailaufnahme der Aktuierung der Wirbelsäulenstruktur (Foto: Daniel Kühn, DFKI GmbH)
Actuation mechanism and rods within the spine (close-up / top view) (Photo: Daniel Kühn, DFKI GmbH)







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