This dissertation discusses the locomotion of modular robots. It is focused specifically on the study of 1D topology configurations (called snakes or limbless robots). The problem to solve is how to coordinate the joint's movement so that modular robots can move both in one and two dimensions.
A big challenge in robotics is the development of a very versatile robot with the full capability of moving on different terrains. This is especially important in applications where the environment is unknown in advance, such as the exploration of other planet's surfaces, navigation in hostile environments and search and rescue operations.
Modular robotics offers the promise of increasing the versatility in locomotion by means of building robots from basic modules. Each configuration has its own locomotive characteristics that should be studied. If the robots have the ability to be self-reconfigurable, then they will be able to change their shapes and topology in order to select the best gait for every terrain and negotiate with different tasks.
One kind of bio-inspired controllers for mobile robots used in the last decade are based on CPG (Central pattern generators), which are a specialized neurons that produce rhythms for controlling the muscle activities of animals. In the steady state CPG behave like fixed-frequency oscillators. For that reason, they can be replaced by a simplified model like sinusoidal generators. The main advantage is that they are extremely simple to implement and requires very few computing resources. Therefore, they can be implemented in low-end inexpensive microcontrollers. Moreover, the generators can also be realized directly as hardware components using either digital or analog electronics.
In this dissertation a general classification of modular robots is established based on their topologies and types of connection. The hypothesis of using sinusoidal generators for controlling the locomotion of 1D pitch-pitch and pitch-yaw modular robots of any length is raised. The results show that this simple model is efficient and the gaits obtained are natural and smooth. It is shown that at least they can move in five different movements. Some of them are totally new and have not been previously studied or implemented by other researchers, from the best of our knowledge. In addition, the relationships between the generator's parameters and the robot kinematics have been obtained.
Another problem is to find the minimal configurations for locomotion, which are the modular robots within the studied groups that have the minimum number of modules and are still capable of moving in one and two dimensions. This problem has been solved and the two minimal configurations are presented. Their kinematics models are studied throughout too.
The experiments confirm that the solutions found to the coordination problem are valid for the locomotion of real mobile modular robots. Four kinds of modular robotic prototypes have been built using the identical Y1 modules, which have been designed specifically for this thesis.
Finally the knowledge about the locomotion of pitch-pitch and pitch-yaw connecting modular robots has been summarized in 27 key principles. |
