Gauge-Based Tip Position Control of a New Three-Degree-of-Freedom Flexible Robot

Flexible robots have given rise to numerous investigations, and their use is easily justified in two main cases: (1) when the weight of the robot has to be minimized and (2) when collisions of the robot with the environment are foreseen, as a flexible lightweight robot delivers less impact energy. Much work has been done by different authors on the position control of flexible robots using feedback of the tip position or tip acceleration. However, the use of these sensing devices is problematic in practical applications of flexible arms: three-dimensional tip position sensing is expensive, and occlusions appear at some arm configurations. Accelerometers cannot be used when contact of the tip with the environment is expected because these sensors cannot stand the high negative accelerations produced at the impact (unless very low speed motions are performed). This paper studies the possibility of carrying out the tip position control of a three-degree-of-freedom flexible arm using sensing devices placed far away from the tip (where contact is expected) in such way that they can easily stand the impact, which will be needed in the development of a position/force control for flexible robots. A control scheme based on motor position sensing plus some strain gauges placed on the arm structure is proposed. Stability of this control scheme is proven and is experimentally verified on a flexible manipulator prototype that was developed in the authors’ laboratory.