Achieving a Fitts law relationship for visual guided reaching

In order to take advantage of the top speed of manipulators, vision cannot be tightly integrated into the motion control loop. Past visual servo control systems have performed satisfactorily with this constraint, however it can be shown that the task execution time can be reduced if the vision system is de-coupled from the low level motor control system. For reaching, there is a trade-off between the accuracy of a motion and the time required to execute motion. In studies of human motor control this tradeoff is quantified by Fitts Law, a relationship between the motion time, the target distance, and the target width. These studies suggest that vision is not used tightly within the control loop, i.e. as a sensor that is servo-ed on, but rather vision is used to determine where the reaching target is and whether target has been reached successfully. Through a simple robotic example we demonstrate that a similar trade off exists between motion accuracy and the motion execution time for visual guided robot reaching motions