I. Introduction
Recent advances in robotics include the capability of planning a suitable trajectory in order to drive the robot from an initial configuration to a pre-determined goal point, or to follow, when possible, a pre-specified trajectory even in unknown environments [1]. Various methods can be adopted to accomplish this task. These methods are mainly classified in relation to the capability of the sensors which are employed to map the environment and the obstacles near the robot. When distance sensors and cameras are considered, the trajectory can be planned without colliding with the obstacles (i.e. no force measurements are required), see [2]–[4].