Department of Applied Mechanics, Adaptive Systems research group

 

Evolution of central pattern generators

 

Krister Wolff, Jimmy Pettersson, Almir Heralic, Mattias Wahde.

 

Project carried out: Aug. 2005 to Jan. 2006.

 

 

Introduction and aim

Many biological organisms are equipped with central pattern generators (CPGs), i.e. neural circuits capable of producing oscillatory output given tonic input. CPGs have been studied in animals such as cats, and there are also observations that support the notion of CPGs in humans.

The development of artificial counterparts to biological CPGs, with the aim of generating robust gaits for bipedal robots, is addressed in this research project. The approach has been investigated through full rigid-body dynamics simulations in 3D of a bipedal robot with 14 DOF.  

 

 

Rendered image of the bipedal robot.

(Scroll down to see movies of the robot walking.)

 

Method

The half-center CPG model was adopted as an oscillator unit, with interconnection paths between oscillators undergoing structural modifications using a genetic algorithm (GA). In addition, the connection weights in a feedback network of predifined structure were evolved. Furthermore, a (massless) supporting structure was added to the robot, in order to guide evolution towards natural, humanlike gaits. Subsequently, this structure was removed, and the ability of the best evolved controller to generate a bipedal gait without the help without the help of the supporting structure has been verified.

 

 

Picture of the structure of the CPG network used in the simulations. Note that an arrow indicates the possibility of full connection (left). The robot depicted with a single hip joint CPG with feedback paths, and a possible choice of connection types (right).

 

Simulations

The simulations were carried out using the EvoDyn simulation library, developed at Chalmers University of Technology. The successful approach involved two phases: First generating a stable gait in 2D with help of the supporting structure. Then, the 2D gait was generalized to 3D, without the supporting structure.

 

Movies of the robot walking in 3D:

long (21.6MB)

short (2.3MB)

 

Publications related to this project

Wolff, K., Pettersson, J., Heralic, A., and Wahde, M.

Structural evolution of central pattern generators for bipedal walking in 3D simulation.

In Proceedings of the 2006 IEEE International Conference on Systems, Man, and

Cybernetics (SMC), pp. 227–234, Taipei, Taiwan, 8-11 October 2006.
IEEE Xplore, CPL,

 

Heralic, A., Wolff, K., and Wahde, M.
Central pattern generators for gait generation in bipedal robots.
In Pina Filho, A. C., ed., Humanoid Robots New Developments, ch. 17, pp. 285–304.
I-Tech Education and Publishing,
Vienna, Austria, June 2007. Invited book chapter.
I-Tech, CPL,

 

Contact information:

Dr. Krister Wolff

Department of Applied Mechanics

Chalmers University of Technology

412 96 Göteborg, Sweden 

 

Tel: +46 31 772 3625

Fax: +46 31 772 3690

e-mail: krister.wolff@chalmers.se