An innovative mechanical and control architecture for a biomimetic hexapod for planetary exploration
- Paper number
IAC-05-A3.2.B.09
- Author
Mr. Marco Pavone, Scuola Superiore di Catania, Italy
- Year
2005
- Abstract
This research addresses the design of autonomous legged robots for planetary exploration. The robot is designed for uneven terrains and is biologically inspired on different levels: mechanically as well as in control.
As far as the robot mechanical design is concerned, a novel structure is developed basing on a careful emulation of the cockroach, whose extraordinary agility and speed are principally due to three major properties:- self-stabilizing posture;
- passive visco-elastic structure;
- specializing legged function: front legs major feature is dexterity, while rear legs generate the major part of forward motion.
Therefore, the structure design enhances these properties, while avoiding an excessive and useless complexity, as follows:
- the robot exhibits a sprawled posture (with a pitch angle of 20 degrees), that provides the obvious advantage of having good stability;
- legs articulate with the body by properly tuned torsional springs (allowing self-stabilizing property) and feet are made of a compliant appendix at the end of the tibia limb and a pair of claws (allowing a better traction);
- the mechanical design of each leg pair is unique: the front legs have three rotational DoF and a pantograph mechanism conferring a high dexterity; middle legs have three rotational DOF too, but a dynamics more devoted to forward thrust. Finally, rear legs are longer and considerably angled posteriorly and have just two DoF, one rotational and one prismatic; the latter one provides the powerful piston-like motion that drives the cockroach forward.
The locomotion control is based on the paradigm of central pattern generator viewed here as a network of coupled nonlinear systems, able to provide an ideal platform to integrate local reflexes and to guarantee robustness and adaptability needed for locomotion control.
Several dynamical simulations were carried out to select the proper dimensions, weights and articulation angles of each leg limb, to tune the position of the centre of mass and to evaluate motor torques needed.
The second major feature concerns the innovative behaviour-based control architecture developed in order to confer the autonomy and adaptability needed to explore unknown environments like planets. The hierarchical control architecture is divided into two levels:- first level devoted to accomplish a reactive control driven by the maximization of a reward function;
- second level devoted to determine automatically the structure of the reward function suitable to accomplish a particular task.
The first level consists of a motor map; the second level is based on a non-associative reinforcement learning aimed to allow the robot to learn how combining sensory information to complete successfully a task. This second level is very useful to face with unpredictable situations like sensor malfunctioning or unforeseen environmental conditions, providing the essential autonomy for the planetary exploration task.
Several dynamical simulations have proved that this novel structure is capable of negotiating successfully obstacles height more than 250% of robot height, thanks to the careful combination of rotational and prismatic actuation. This is a very good result if compared with the existing hexapod robots.
Moreover, it has been proved that the high level control architecture developed is able to successfully face with sensor malfunctioning.
To sum up, currently robot simulations are encouraging; at the IAF congress are planned:- real-time simulations on Earth and Mars surfaces with robot climbing obstacles and negotiating extremely harsh terrains;
- since the hardware realization is going to begin in a short time, we are confident to show the real robot in action!
- a poster that resumes step by step design, realization and the major features of the robot proposed.
- Abstract document
- Manuscript document
IAC-05-A3.2.B.09.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.