Wide bandwidth positioning systems for space and underwater vehicles

This paper presents a method for wide bandwidth stiff position control of unmanned underwater and space vehicles. We start by arguing that the use of feedback alone may not provide an underwater or a space vehicle sufficient bandwidth with large stiffness. In other words with feedback alone the vehicle may not behave like a stiff platform in the presence of a wide frequency range of disturbances. Given this limitation, we suggest that the vehicle must be connected to environmental structures by means of cables or grabbers. These connecting cables will develop dynamic and kinematic constraints on the vehicle motion. This problem led us to develop a method that allows for control of the motion of constrained underwater or space vehicles. This method is called Impedance Control [1],[2],[3]. The frequency domain essentials of Impedance Control and a robust controller design method are given in reference [3]. We explain how, with the help of this method, a vehicle connected to a structure by means of cables can be positioned with high stiffness while at the same time the cable tensions are also under control.