  A reactive obstacle avoidance method for mobile manipulators is presented.
The objectives of the developed algorithm are twofold. The first one is to find
a trajectory in the configuration space of a mobile manipulator so as to follow
a given trajectory in the task space. The second objective consists in locally
adjusting the trajectory in the configuration space in order to avoid
collisions with potentially moving obstacles and self-collisions in
unstructured and dynamic environments. The perception is exclusively based on a
set of proximity sensors distributed on the robot mechanical structure and
visual information are not required. Thanks to the adoption of this kind of
proximity distributed perception, the approach does not require a 3D model of
the robot and allows the real-time collision avoidance without the need of a
sensorized environment. To achieve the features cited above, a behaviour-based
technique known as Null-Space-Based (NSB) approach has been adopted with some
modifications.On one hand, the concept of a total pseudo-energy based on the
information from the distributed sensors has been introduced. On the other
hand, a method to combine different tasks has been proposed to guarantee the
smoothness of the realtime trajectory adjustments. Another significant feature
of the method is the strict coordination between the base and the arm
exploiting the redundant degrees of freedom, that is a relevant topic in mobile
manipulation.
